CAA FAA UK based 737 TRE
 

Perhaps asking for too much but here goes..

My b737 300/400/500 LPC has expired (last LPC was Jan 2011, did an OPC in July 2011) I wish to renew my LPC ( perhaps the correct way of saying this is that i wish to renew my instrument rating)

Here's the longshot. I have taken the FAA ATP (part 121) writtens and have a current class one FAA and CAA medical, I need only take a FAA ATP check ride to give me a FAA ATP. Is it in the realm of possibility that I could renew my JAA LPC (IR) and do the ATP check ride at the same time?

Only if the FAA examiner happens to also be an approved JAR TRE and the sim you use is both FAA and JAA approved.

For info OPC doesn't count for anything other then remaining current within the company you were in. For licensing purposes the only important date(s) are those of your LPC's.