Fast Track Security at Heathrow Airport Departures?

My partner is disable and we have booked a flight with British Airways in business class to make his long journey more comfortable.
Is it true that business class allows him to go through Fast Track Security?
Does that mean he will have less waiting time at the security checkpoint?

You get through security on an expedited basis if you have wheelchair assistance. I don't know if that covers "Fast Track Security" (not familiar with it) but you will get through a lot faster than the main line.

Yes and wheelchairs get some priority

Ask heathrow, how would we know?

Fast track at most airports is an illusion. You may get past the immigration reasonably fast, but Customs and Quarantine will not get you through any quicker.

Call the airline right now and TALK to them about this. As @Rona says, they can't guess exactly what you and your partner need and don't need. If you need any special consideration you MUST arrange it in advance, or be prepared to wait for possibly quite a long time.