Facts:
4. The applicant is an Indian national, born in June 1990. She came to this country with a Tier 4 (General) Student Migrant visa, valid until 30 October 2013 and then extended until 31 May 2014. The day before it expired she applied for a further extension, on the same basis, but that was rejected in July 2014, with a right of appeal which she exercised. 5. The First-tier Tribunal (FTT) rejected her appeal, in a written decision dated 24 November 2011. The judge decided that the applicant had not made her case that she had adequate funds; a loan agreement she produced was not in her name. Her case had not been adequately made. On 2 December 2014, she applied for permission to appeal against that decision to the Upper Tribunal (Immigration and Asylum Chamber). 6. While awaiting the outcome of that application, on 28 January 2015 she moved from [ ], Newcastle-upon-Tyne, to different accommodation at [ ], also in Newcastle. The same day, her then solicitors wrote to the FTT by fax, notifying the change of address. An authority to act signed by the applicant was enclosed. The fax number used (ending 987) was the one designated as “IAFT4 (Permission to Appeal)” at the time, in the FTT’s guidance for users. 7. On the same day, the solicitors emailed the customer services email address of the “IAC” (Immigration and Asylum Chamber) of the FTT, notifying the change of address but without the signed authority to act. On 2 February 2015, IAC emailed back saying that the request to log the change of address could not be processed without a signed written notification of authority to act as legal representative. The email also gave an address and a different fax number, ending 895, designated as for “General Correspondence”. 8. On 3 February 2015, the solicitors repeated their request, enclosing the signed written authority to act but sending it to the “Permission to Appeal” fax number, ending 987. They did not, as they should have done, fax that letter and the signed written authority to the “General Correspondence” fax number, ending 895. So the change of address was not registered with the FTT. 9. Then, on or before 19 February 2015, the FTT refused the application for permission to appeal. Notification of the decision was sent by post to the applicant’s old address at [ ], together with reasons for the decision which I have not seen. The applicant did not receive the notification letter, having moved to [ ]. The letter also mentioned the right to apply to the Upper Tribunal for permission to appeal. 10. The FTT’s decision has been assumed by everyone in this case to have been validly promulgated and effective and binding on the applicant from 19 February 2015, even though the applicant knew nothing about it until months later. The decision was, indeed, sent to the address at [ ] which was the only address accepted by the FTT as an address of record for the applicant. 11. On that assumption, on expiry of the time limit for making a further application to the Upper Tribunal for permission to appeal, the applicant became “appeal rights exhausted”. The time limit expired on 6 March 2015. The consequence of that was she was, and is, regarded by the respondent as having become an “overstayer” from that date. She did not know this at the time and nor did her solicitors. 12. On 18 June 2015, having heard nothing, the solicitors emailed the IAC customer services email address referring back to the previous correspondence, expressing concern that “you may have sent correspondence to our client’s previous address” and asking what was the status of “our client’s appeal (IAFT-4) and when we can expect to receive a decision on same”. That email was not copied to the respondent. The FTT did not reply to it. 13. The applicant, not knowing she would be regarded as an overstayer, decided her best strategy was to withdraw her application for permission to appeal and instead to make a fresh application for leave to remain as the unmarried partner of a Tier 2 Migrant. On 14 July 2015, her solicitors wrote to the FTT, again to the fax number ending 987, saying they had “instructions to withdraw her appeal with immediate effect”. This must be taken to refer to the application for permission to appeal that had already been refused. 14. There is no evidence that the FTT ever responded to this request, which from its perspective would be academic since the application had already been refused, though it was evident from the request to withdraw that the solicitors were unaware of that. The applicant, under the same misapprehension, applied on or about 12 July 2015 for leave to remain as the unmarried partner of a Tier 2 Migrant. She made an appointment to attend personally, paying a fee for the “premium service”. 15. On 15 July 2015, she attended the appointment with her partner. She met the respondent’s case worker, Mr Christopher Duncan Wood. She produced documents to show a subsisting relationship with her partner of at least two years’ duration. These are the documents in the first exhibit to her witness statement. The documents were a tenancy agreement, bank statements, joint account bank statements, utility bills, photographs, letters, appeal letters and the solicitors’ letter seeking to withdraw her appeal. 16. The case worker went through the documents and asked the applicant to provide further documents, to show a genuine and subsisting relationship covering the period from February to August 2013. He said nothing about the applicant being an overstayer. I infer that he may not have known about the FTT’s decision and may not have checked the position at the time. But the respondent as an organisation, the Home Office, knew of it then or soon afterwards, because it relied on the FTT’s decision just over a month later. 17. The applicant provided the requested documents by post, about a week after the appointment. These are the documents in the second exhibit to her witness statement. The documents dated from the period from February to August 2013, to which reference had been made by Mr Duncan Wood, the case worker. They were prints and photographs from gmail conversations, a car rental receipt, uploads and posts on Facebook, telephone bills and further photographs and letters. 18. On 21 August 2015, the respondent wrote to the applicant refusing her application. The refusal letter was in the name of Mr Duncan Wood. Among the reasons for the decision was the news to the applicant that her permission to appeal application to the Upper Tribunal “was refused on 19 February 2015, and your Appeal Rights were exhausted on 06 March 2015”. That was how the applicant found out about the FTT’s decision. Mr Duncan Wood went on to explain that the application had been made 130 days after expiry of the applicant’s leave to remain and was therefore refused. 19. The reasons also included reference to the first tranche of documents, but not the second tranche which Mr Duncan Wood had himself requested. He went on to say in the decision letter that “[b]ased on the above”, i.e. based on the first tranche of documents, “it is not accepted that you have provided evidence to show that you have been living together in a relationship akin to marriage for 2 years prior to your application on 15 July 2015”. 20. The decision letter included advice that the applicant could seek an administrative review if she thought an error had been made. She sought administrative review. The application was submitted online on 3 September 2015. Her solicitors helped her complete the part of the form giving details of why she contended that the respondent had “applied the Immigration Rules incorrectly”. The solicitors addressed each of the two grounds of refusal separately. 21. They explained the misapprehension about the status of the application for permission to appeal and the request to withdraw the appeal made under that misapprehension; and pointed out that the case worker had been shown the letter requesting withdrawal. They said the case worker should have “considered the background and considered exercising discretion for the delay”, given that the applicant did not know she had stayed beyond the 28 days after exhaustion of appeal rights that are normally disregarded. 22. The solicitors also pointed out that the second tranche of documents had been returned with the refusal letter, proving that they had been received after being sent by recorded delivery. Despite that, they pointed out, it was clear from the refusal letter that the second tranche of documents “was not considered at all”. Yet the evidence sent “clearly demonstrates that the relationship had been subsisting for the required time …”. 23. The administrative review application did not succeed. The response was a letter of 17 September 2015 stating that the applicant should leave the United Kingdom, or she would be liable to be detained and removed and could be prosecuted. The reasons given restated that the applicant had become an overstayer after the FTT’s decision and that the applicant had not demonstrated the necessary two year relationship with her partner. The reasons did not engage with the points made by the solicitors in the administrative review application. 24. They included repetition of the statement that the FTT’s decision meant the applicant was “appeal rights exhausted” from 6 March 2015. They stated that the respondent had “no evidence that your appeal was withdrawn”. Further, the reasons stated, based on the first tranche of documents only – there was no mention of the second tranche – that the applicant had not shown the necessary two year relationship. The result was therefore that the original decision was maintained. 25. After that, correspondence and the present judicial review claim ensued. The next few years saw the matter proceed through twists and turns at the permission stage. This took an unusually long time, as I have said. Permission was at first refused in this tribunal but was eventually granted by Singh LJ and Henderson LJ on 17 May 2018, for reasons given in Singh LJ’s judgment given that day, with which Henderson LJ agreed.