Originally Posted by
shorthauldad
3h is actually the MCT between LHR and LGW, isn't it?
Don't know for sure, but 3 hours could be tight. It could take 45 mins-1 hour to go through immigration, collect your bags and get to the bus stop (as non-EU passport holders which I'm assuming the OP is). It's unlikely that the bus will leave exactly as you board it so you could add 15 minutes as a contigency.
Then, it could easily take 1 hour to get to LGW from LHR, due to traffic on the M25.
Given that you probably have to check in at least 45-60 minutes before hand for your next flight, it could be very tight indeed.