Depends how many nights you want parking for. Jurys Inn at Hatton Cross does a park and fly package but it's for 8 or 15 nts. The tube station is across the road.
Thanks again, but looking for somewhere to stay over that has easy access to central London, so needs to be near a tube station, and on site parking overnight to go to Heathrow in the morning.
Chiswick is a good place to stay, 20 minutes in tube to Central London and being at the start of the M4, a 20-30 minute drive to Heathrow. A nice hotel is The Chiswick Moran.