I think you need a valid Multi IR to start the training, not sure about the Multi Eng but dont think it needs to be valid.\
Best bet is to ask your TRTO. Or as IRRenewal says try Lasors, think its in section F.
Andy
Edit:.....
Yeah just checked to start training you need a valid and current Multi IR, 100 hrs P1, MCC, and ATPL exams.
All in
http://www.caa.co.uk/docs/175/SECTION%20F.pdf
Hope that helps