I know a couple of people who have obtained an IMC this way, just by writing in, no exams requried!
That's correct. You need to have had an IPC within the previous 2 years (IOW the CAA does not recognise the FAA IR rolling currency self-validation). Send a cheque for about £80 to the CAA and they give you the IMCR. Mind you, you do need to have a UK PPL and a UK medical too.