Easy 20% Reduction
The number of routes has not really changed, other than the loss of the Athens and Cagliari routes...
The other reductions have come in the way of frequency reductions...
As I am not able to view last years timetable to compare against it is very difficult to say exactly where the reductions have come from...
The domestic routes to Beflast, Glasgow and Edinburgh definately seem to have taken a cut! These routes use to operare 4-5 times daily, and now EDI is 3 x daily, Belfast City 2x Daily and Glasgow 3-4x daily.
Other routes could have been cut a while back, but not noticed...
But I remenber previously cites like Budapest and Alicante had 2 flights a day and this is now a single rotation. Paris and Amsterdam use to be 4x daily and now 3x daily. Barcelona and Geneva are only 2x daily, these use to be up to 4 rotations previously.
These are just off the top of my head, I do however know over the last few years a number of major cities have seen a reduction in services from LTN, since they have started to offer the cities from LGW. With the drop in frequencies they had instead increased the number of destinations.