Heathrow does not anymore. Some people now stand on the top of the car parks but you are likely to get moved along. Most people just park up on the road side at the end of the runways. Shame, as a large number of European airports do have good viewimg areas.
Heathrow's viewing gallery (which had a VERY expensive admission charge) was closed many years ago on security grounds. Here's the relevant link for unofficial viewing areas:
http://www.plane-mad....eathrow-lhr-egll.html
Hi Chris, when I went to Heathrow in 1965 it was free. Been many times since but not to viewing area. They will charge for anything if they think that they can get away with it these days.
You need to check the wind direction before you decide where to pitch up. If the wind is in the east, you can see take offs over the car park at Hatton Cross tube station. If the wind is in the west, you can see take offs from the southern perimeter road (only if they`re using the south runway). The plane spotters seem to favour the petrol station there. You won`t see anything if they`re using the north runway for take offs though.