If the rating has expired by more than 5 years, but less than 7 years (i.e. it is more than 6 years, but less than 8 years, since the last test) then you need to do training as required and a test with a full-time CAA staff examiner. The test has to be done in an aircraft, but some of the training can be done in an FNPT2.
If it has expired by more than 7 years, then you have lost your ATPL ground exam credits and you have to do the whole lot again!
Linda Mollison