They use a combination of A310s and B737's on LHR-IST.
The B737's essentially just have a table across the middle seat in J, so it's not great, but the A310's have 'proper' club seating.
The International part of IST has been completely refurbished of late & is very pleasant, although I've never had long to wait for flights.
The long haul services are on A340s. They have a bar in J class - one of the few to offer it, I guess.