Do all these fast fighter jets have a civvy-compatible transponder, and will they show up on a civvy TCAS
Yep you can get a traffic traffic when they fly under you when your at 1000 agl.
I doud't very much if they would speak to you and if they did the person you would be speaking to wouldn't be able to give you any service as more than likely they won't be a controller or from the UK and won't have a clue what a basic service is.