Tried to do my homework on PPRuNe and came across these:
http://www.pprune.org/forums/showthread.php?t=44985
http://www.pprune.org/forums/showthread.php?t=260130
But they don't quite answer this: when will a major airport like LHR introduce restrictions due to the wind like during the recent fog mularkey?
Currently see winds 248 at 15 gusting 26.