Just to add another reference point on a delayed price guarantee claim. Along with another thanks to the forum!

Booked a flight on Sunday evening, read the price guarantee post on this thread so submitted a claim on Tuesday morning. Received a reply this morning, apologising for the delay in replying (!) and including an £80 voucher.

Ended up being £180 return LHR to JFK, less than the price of the train to London!