By 1500 quid??

A full J LHR-EDI is £400 return. But these seem to be booked in cheapy class.

When were these intially booked? To get the T fare, it is 21 days advance purchase. So I wonder if they combined a fully flex W with the L/V domestics and did them as add ons (or is the term sectorised it?) and that's causing the problems.

To the OP, I really think you need to tear into your TA. Get them to send you a fare break down or put your PNR into viewtrip.com/checkmytrip.com and see if there is a fare break down on the e-ticket receipt.