Heathrow to Gatwick transfer by bus?

[OhBling]

I have 4 and a half hours from landing in heathrow to taking off at Gatwick early in the morning in July. I won't have any luggage and can check in for the Gatwick flight online in advance so in theory, I just need to hurtle from one to the other. I'm thinking of taking the bus and they say it takes an hour - anyone have any experience with this? how accurate is that and how reliable?

I did this years ago (2001) and it was problem free.
I could not speak for how it runs today though.

I got the LGW to LHR bus in May. You will have plenty of time and yes it takes around 1-1 1/4 hours. Was problem free.

Okay. thanks. I'm so scared - DH will never forgive me if I miss the flight from Gatwick because my girls trip got delayed...!