In R (on the application of Bah) v Secretary of State for the Home Department IJR  UKUT 518 (IAC) the Upper Tribunal finds that even though the applicant had received a letter stating that the Home Office “aimed” to resolve cases by July 2011, this did not amount to an unambiguous promise because the letter went on to imply that some cases might not be. You can get a flavour of the reasoning from paragraph 42:
I do not accept that the words: ‘your’, ‘will’, ‘be’ and ‘deadline’ made this letter a letter by which a specific promise was given to review the case by July 2011.
Signing in blood with God as an actual manifest witness probably wouldn’t have worked either. For further reading on The Legacy see earlier post: Legacy cases “laid to rest” by Court of Appeal.