Thanks all for your input so far.

The flights would of course be connecting flights (thats the purpose of specifying the MCT!!!) and the airlines would be responsible for reaccomodation in case of misconnections.

However, the purpose of the MCT is to specify a minumum period within which a normal person can realistically make a connection. Therefore if the MCT is achieved (on paper for sales purposes and on day-of-ops for practical purposes) it is assumed that the passenger is able to make it for the next flight. Obviously extraneous circumstances are factored in at times (eg. M25 pileup), but in general this is the principle behind it.

From the airline perspective, there is a double edged sword. Obviously a low MCT gives the opportunity for higher sales and more city pairs, but an unrealistically low MCT creates exponential increase in workload and cost by virtue of misconnection management.

We advise passengers to use the National Express coach service between Gatwick and Heathrow for their transfers, and the elapsed time between Gatwick South and Heathrow CBT (including waiting time for the bus) averages around 90 minutes. Assuming a 60 minute closeout at departure airport (normal) and a 30 minute connection from CBT to Terminal 4 (pessimistic), we are already at 3:00. By specifying a 4:15 MCT, that leaves 1:15 to clear immigration and collect bags, which my experience says is extremely doable at both LGW South and LHR T4.

Looking deeper into the OAG MCT tables, specifying a 4:15 MCT exception will actually put us as the highest active MCT published for the routing (the 4:30 MCT is for AA flights to/from LGW which is no longer active since AA doesn't operate to Gatwick anymore). It puzzles me to see how someone like BA or IB can realistically expect passengers to make the LHR-LGW vv transit in 2:30 or even 3:00.