Thanks all and in particular Billiebob - it looks like the 6 month window is the issue. You'd think it would be training as deemed necessary if you were to come back to the test in future though I won't test the issue!
One other area of note - the CAA state a flight training course that includes at least 2 hours and 30 minutes of dual flight instruction under normal conditions of multi-engine aeroplane operations, and not less than 3 hours 30 minutes of dual flight instruction in engine failure procedures and asymmetric flight techniques.
Is the 'flight instruction' mandatory to be in a/c or can some of the 6hrs be done in a sim? I'd have thought there's some benefit of running through the engine failure procedures in particular in a sim? As FTO's seem to price for 6 hours MEP across the board I assume this isn't worth exploration but any advice appreciated.