Other Middle East and Africa Frequent Flyer Programs - Fasttrack Access at LHR T3

I am a silver card member and I travel frequently through LHR with GF and usually on flights out of LHR on Y class, GF offers an invitation to their lounge along with fasttrack access which I always thought was a great addition to their FFP programme. However I have noticed recently that everytime I go through fastrack the staff that inspect your travel documents send me back since my boarding pass says Y class despite having the fastrack invitiation. Does anyone know anything about this, or are the folks at LHR trying to find additional ways to make Pax's lives more difficult (as if it isn't difficut enough already to have to travel via LHR!)

Thanks!

I'd thrust the fast track invitation in their faces and keep on walking..

That would make my big collection of fast track invitations useless :(