not sure, but from what I've read elsewhere on this forum, 110W+ is illegal and will fail MOT, or at least get you pulled over when the police car coming the other way can't see anything for the blinding light in his face!
the best replacement seems to be Xenon 55W bulbs (easily found in Halfords). They're the same wattage, but a bit brighter than normal. I've tried them and I <think> they're better than standard. certainly not as yellow.