Thanks again to all for their input. As mentioned earlier, we do not and will not recommend that passengers use anything other than the direct National Express coach service between Gatwick and Heathrow. This is blocked at between 60-90 minutes depending on time of day. We would accept responsibility for passenger misconnections resulting from any delays to that service, but simply cannot do so in case of passengers trekking through half of London on three different modes of transport.

We have taken the decision now to publish 4:15 as our inter-airport MCT. While I would personally prefer 4:30 keeping in mind our typical passenger profile, unfortunately the demands of connectivity simply make anything over 4:15 unworkable. Therefore, they must forego duty free and run to the gate instead.