OK, just to close off my side of this debate...

1) The YQ surcharge applied was lowered, presumably by taking the YQ for the BHX-BRU point to point and adding it to the same for the BRU-ORD

2) Having torn a strip off the ICC yesterday, I noticed that I was waitlisted for the TATL flight. Later this afternoon (after Chicago woke up I guess) the flight went to confirmed. An hour or so later the ICC supervisor I spoke to yesterday called me and apologised, explaining the seat was reinstated.

So in summary, the £80 I saved in YQ was then countered by a degree of hassle and wasted time on my side. Crazy that they can't sort out this seemingly recurring problem, although the first time I've had an issue.

Here's looking forward to my test drive of seat 1K on a UA 767.

Edit - No, just looked and they've charged me the original YQ, not the adjusted one as promised. This really must be the Ryanair of FFP's, but like Ryanair (which many of us wouldn't dare set foot on) we tolerate it because it's so damn cheap.