Came through LHR twice last week.

First time was through the FCC T3-T4, but I was very early in the morning, having been in the first set of flights that landed right after the 6:00 a.m curfew. Had no lines at all and walked right through the FCC security.

Second time was T4-T3 at about noon on Sunday, but landside, since KLM wouldn't check my bag through to UA. No line at the T4 immigration and 5 minutes max at the T3 "fast track" security, although the regular lines didn't look much worse.