David you need to do an ATPL skills test. It is essentially an LPC with the additional requirement of a manually flown, raw data ILS. If you're on the 'bus that means manual thrust aswell!
You will need to ensure the examiner fills out the appropriate skills test form - you can download this from the CAA website. They will also require your logbook or a printout of your hours if you use skylog, with each page signed by you. It is also helpful to get your airline to include a covering letter confirming the hours you have completed with them.
It's also worth checking LASORS to check the hours requirement and to make sure you fill the application form in correctly. Again this is available for download from the CAA website.