Gatwick to London City Airport

Well it's going to be tight and obviously depends on your Gatwick flight not being delayed. Do you have bags to check? London City is not a big airport and well connected to the Dockland Light Railway. From Arriving at London Bridge you can get to the airport in about 20 minutes. If I didn't have a bag to check and had pre printed my boarding pass I would aim to arrive 1 hour before my flight.

Is this a single ticket booking?

When does your flight from LCY close boarding? Some airlines close boarding 30 minutes prior to the scheduled departure time.

Do NOT stop to smell the roses.

Best wishes for a successful transfer.

Getting out of Gatwick is likely to take an hour minimum. I rarely get out of there in much less than 45 minutes even arriving at midnight. I have an electronic passport and can therefore use the quick channels. If you have to join the queue for non EU passengers, you could add half an hour.

You will need to be at City an hour before your flight.

There are lots of trains to London Bridge, so you should not have to wait more than 10 minutes for a train. Some trains are quicker than others. Say 2+ hours from arrival to London Bridge, so it’s 12.35. You then have a tube and a DLR element. You need to be at City airport at 1.20. It should be possible, but it’s tight and is reliant on your inbound flight being on time, no passport line holdups, all three public transport options working without any holdups and you navigating a transport system that you don’t know with jet lag. Personally, I would want more slack in the schedule.

If you are booked on a through ticket, it’s of less issue, assuming there is a later flight to Prague from City, as the airline will be responsible for getting you there.

Single ticket carry on only check in cut off at London City is 20 minutes before on all flights wth British Airlines City. True this is not my ideal scenario, but the alternative was a 9 hour lay over at Gatwick.