On Fri 16th Dec between 20:00 and 21:45 there were up to 15 aircraft holding at one time, split between GROVE, CHASE and WELIN.
The Met Office failed to put any mention of fog on the BHX TAF for the early part of that night, which could have warned crews in advance to carry more fuel for holding and could have pre-warned ATC
The fiasco was caused by a combination of; fog not forecast, a large number of inbounds, full ILS only available on the one end that had the worst RVRs and a mix of aircraft in the hold requiring a range of different minimum RVRs. At one point there were two aircraft diverting away due to low fuel, with one aircraft diverting in from East Midlands who got a fairly quick approach! Also, Manchester and London were not very co-operative when BHX aircraft requested diverts away, probably because they were at full stretch too
London and Birmingham ATC did their best, but were clearly struggling at times with the situation, a situation that has probably never occurred before
Lots to be learned from this and hopefully this situation will not happen again