Heathrow has grown so big the surrounding infrastructure is almost at a standstill. I'm surprised it's still so popular given the gridlock.
That's a gross overstatement. Like many here our office is there and I drive constantly on the M4 and M25, use the Underground, etc, and the liability to delay is no more than you find in comparable areas. My journey time expectations are more reliable there than elsewhere. It's airside that it's gridlock.
You want to try the M6 from Coventry to Wigan (100 miles) on a Friday afternoon for infrastructure overloaded !