WHBM

Hello from London, where these questions come up from time. It is always useful to give your actual itinerary and airlines. For example in the first question we don't know if the travel is arriving UK domestic or international. Likewise, if you have bought a through ticket (in which case your bags will go through as well) or two independent tickets (in which case you have to wait for your bags, exit, go to the check-in counter, and start again).

Any airline that sells a through ticket knows what the appropriate minimum connecting time is, because if the connection is missed on a through ticket they are in for all sorts of additional costs to reaccommodate you, which, if nothing else, absorbs all their profit. So if it is an allowable Minimum Connecting Time, then it will be reasonable.

2 hours 25 minutes for the first one is fine, just follow Flight Connections and you will be transferred by a bus between the terminals. It's quite a distance between Terminals 5 and 3 but the bus gets through fairly promptly.

For the second one, 1 h 50 m is normally OK, again it depends if you are connecting to a UK domestic flight (NB this includes flights to the Irish Republic as both countries operate a Common Travel Area) as in this case you will be directed through Immigration, which is often the step with the longest queueing. Terminals 3 and 1 are adjacent but the transfer bus makes a short connection.

Regarding not stopping for eating or shopping, normally that is fine when done in the final departure terminal, when you have gone through all the steps and can see how much time is left. There are not a lot of opportunities beforehand anyway. Don't forget to tell the waiter in any restaurant what time you have to be out again - they are of course completely used to this. Payments for anything, if you are just passing through the UK, need either a standard credit card or UK cash.