Helicopters over central London
Thanks for kind replies to previous two queries, here's another for you.
Is it true that helicopters flying over central London have to stay above the River Thames - or, given how twisty the river is, pretty much along its line?
If that is so I then would be interested to hear why that is. Excuse the bad taste but is it only to give the 'copter something to crash into other than streets and buildings with people in?