It's not fast, I was there last Monday. Probably took about an hour in total to clear security and immigration - grand total of 3 out of about 8 lanes open.

Business pasengers can Fast Track through security but you can't Fast Track the queue which holds you at the upper level before going down to security, and it doesn't help you at immigration at all.

I had a 3 hour layover last Monday between my LHR-DUB and my connecting Newark flight and I still only got 20 mins in the preclearance lounge.

What went wrong was that they had started pulling people out of the queue who were missing their flights. However, there were more of these people than available agents, so the rest of us were actually getting continually pushed up the queue rather than down it. You could suddenly find you were further from the front than you were 10 minutes previously.