AJC wrote:

More details: the plane is supposed to arrive at Heathrow a little
before 11 a.m. GMT, and is supposed to depart Gatwick at 1:45 p.m.
GMT.

Who sold you this connection? Last year BA were quoting a minimum
connecting time of 3 hours via the inter-airport coach. It looks like
you will be using a very expensive taxi.
--==++AJC++==--

Well, it arrives at 11 AM, that only 15 minutes shy of 3 hours, plus
they said "a little before 11", so it could be only a 5 or 10 minute
difference.