I travelled through T1 yesterday and was not impressed.
Security is stricter than at MME, you have to stand in a specific point to get your photo taken, (happens as you hand over your boarding pass at MME), you have to take shoes off at LHR, not MME, there is no space to put shoes back on so blocking access for others coming through.
Edit - note, I have no problem with security, but would like some consistency...
When you finally get through, you then have a long walk and another boarding pass check to get through to the domestic departures.
BMI wouldn't let me in the lounge, MME did, yes it was a cheap ticket so guess it was a bonus at MME.
LHR is scruffy, dirty and generally unpleasant.
I have flights booked each month until Christmas, but will be travelling home by train in future, it is easier in the long run.
Oh, and just for a change, the flight was delayed....