Trails
I use and contribute to Planeplotter. Having been watching aircraft for 57 years I can say that, even with the after effects of 9/11 and the world economic downturn, the number of flights over UK and Irish airspace has increased during the last 3 years or so and the levels are pretty much equalling the all time high.
West Wales is a happy hunting ground for both RAF AND USAF aircraft which do not show up on FR, some do on Planeplotter. Also there has been a significant increase in direct routings to Atlantic Ocean entry points for traffic out of mainland Europe and a not insignificant number of LHR departures, all which not many years ago would have been tied to airways. As I'm typing there is an example of a very short haul flight from LHR to DUB over Builth Wells at FL320. He will exit the UK on a direct track to DUB over Aberystwyth. He is on FR and, given the weather tonight, will be pulling a contrail. In days gone by he, and the Atlantic bound traffic would have routed either via Brecon and Strumble or via Wallasey. At the same time there are 4 other Aer Lingus flights visible that have followed, or are about to follow, a similar routing. Further south there is a Kerry to Stansted Ryanair flight at FL390 over Haverfordwest.
This year these islands have had much better weather than the previous three summers. From my vantage point on the west coast of Ireland I've sighted far more aircraft trailing this year than for many years previously both on airways and on direct routings. Primarily this is because of the predominance of winds on the Atlantic favouring flights crossing my airspace, the temperature gradients being conducive to contrail formation over a wide range of flight levels and, of course, far more days with reduced or zero cloud cover. Most aircraft have shown up on Planeplotter, far fewer on FR, and there have been times when three or four Delta B767-300s have been sighted at the same time and these do not show up on any plotter. What the OP is observing is nothing more than the average day's use of part of the UK's increasingly crowded airspace.