MCF v The Secretary of State for Defence

This is an appeal, with my permission, against the decision of the First-tier Tribunal which sat on 14 March 2025.

I shall refer to the appellant hereafter as “the claimant”. The respondent is the Secretary of State for Defence. I shall refer to him hereafter as “the Secretary of State”. I shall refer to the tribunal which sat on 14 March 2025 as “the Tribunal” and the tribunal to which I am remitting the matter as “the new tribunal”.

The claimant appealed against the decision of 17 April 2023 that his conditions of polycythaemia rubra vera (PRV) and myelofibrosis (MF) were not attributable to his service and were not aggravated by it. The claimant had not raised a reasonable doubt based on reliable evidence that that the conditions were attributable to or aggravated by his service.

The matter came before the Tribunal on 14 March 2025 when the claimant appeared with his wife and his representative and gave oral evidence. A presenting officer appeared by video, although technical issues meant that he could not be heard and the appeal proceeded without him. The appeal was refused and the decision of the Secreta of State upheld. The Tribunal issued its statement of reasons on 3 April 2025.

Permission to appeal was granted by District Tribunal Judge Sellar on 25 May 2025, although the claimant considered that to have been a limited grant of permission to appeal.

On 17 October 2025, to the extent that it was not encompassed by the existing grant of permission to appeal, I acceded to the claimant’s application and granted him permission to appeal. It seemed to me that there was an arguable case that the Tribunal erred in law for the reasons set out in his grounds of appeal.

On 21 November 2025 the Secretary of State provided submissions and supported the appeal. The Secretary of State agreed with the following grounds, as set out in the claimant’s application for permission to appeal, which were summarised for the purposes of the application:

whether the Tribunal had correctly applied the causation test

inadequacy of findings in respect of latency and delay between service (which ended in 1989) and diagnosis (PRV 2002, MF 2020)

whether the admission of the scientific papers by the medical member constituted an arguable error of law.

The remaining grounds were summarised below:

the Tribunal’s failure properly to consider the statistical likelihood of two submariners both developing PRV and MF and dismissal of the significance of their shared service and cabin

dismissal of evidence regarding the other submariner’s similar diagnosis and failure to consider the statistical data on the rarity of both conditions

not adequately considering that all crew members on a submarine shared the same air, increasing the likelihood of similar exposures and outcomes.

With regard to the latter 3 grounds of appeal, the Secretary of State considered that, while two submariners having rare conditions might seem significant, small sample sizes could produce coincidental clustering. Without controlling for other factors, the shared cabin was not proof of causation. Rare illnesses could still occur independently. Statistical rarity did not establish a causal link without evidence of a mechanism or exposure pathway. Common air supply did not guarantee identical outcomes. Individual differences and lack of proven harmful agents made that argument speculative.

In summary, the Secretary of State considered the remaining grounds to be immaterial. Having reviewed the entirety of the response bundle, the Secretary of State supported the claimant’s appeal and requested that the original Tribunal decision was set aside and remitted to a freshly constituted tribunal.

On 13 January 2026 the claimant agreed that the appeal should be allowed and the matter be remitted back to a new tribunal for a fresh de novo hearing.

Neither party has sought an oral hearing and I do not consider that it is necessary to hold one in order to resolve the matter. Both parties have also consented to a decision without reasons under rule 40(3) of the Tribunal Procedure (Upper Tribunal) Rules 2008.

For the reasons identified by the Secretary of State, I am satisfied that the Tribunal made errors of law which were material to the decision and for that reason the decision of the Tribunal should be set aside.

In the circumstances I do not need to consider whether the Tribunal made any other errors of law.

I am satisfied that the resolution of any other grounds of appeal will fall to be subsumed at the hearing before the new tribunal.

I therefore allow the appeal and set aside the decision of the Tribunal. I remit the matter to a new tribunal which should conduct a complete rehearing of the matter.

I must stress that the fact that this appeal to the Upper Tribunal has succeeded should not be taken as any indication as to the outcome of the rehearing by the new tribunal. It is quite possible that the new tribunal may end up effectively coming to the same decision as the previous Tribunal. Alternatively, it is possible that the new tribunal might take a different view of the facts and reach different conclusions from that of the Tribunal.

It is for the new tribunal itself to decide which of these alternative options open to it applies, depending on the view it takes of the facts and providing it makes proper findings of fact and gives adequate reasons. It would not be appropriate for me to express any opinion either way on the merits of the appeal.

The following directions apply to the hearing before the new tribunal:

The new tribunal should not involve any member who was a member of the Tribunal involved in the hearing of the appeal.

The new tribunal must considerand make relevant findings as to whether or not the claimant’s conditions of polycythaemia rubra vera (PRV) and myelofibrosis (MF) were attributable to his service or were aggravated by it and whether the claimant has raised a reasonable doubt based on reliable evidence that that the conditions were attributable to or aggravated by his service.