It seems the spotter-friendly scrooges at London Heathrow have come up with a fantastic scheme to encourage people to use their visitors centre, and to encourage the spotter community in general.
The prices to park at the visitors centre, which is the only official viewing location following the closure of the Queens Building terrace a number of years ago, are set to increase. They are as follows:
£2 per hour
£10 per day
This is not cheap. Therefore we suggest you park elsewhere (Hatton Cross tube station is a slightly cheaper option), or use public transport entirely.
Remember, buses that travel around the perimeter of Heathrow are free to use, and stop at Hatton Cross. So you can get the tube in from elsewhere in London and get to the visitors centre free on the bus.