Are there any holidays for Brits wanting to travel with other TG people? I mean relaxing and interesting holidays not sex trips.

Not aware of any as such, but you might try the many t-girl events at hotel like Eastbourne. Bournemouth,Harrogate and so on, there is a week long event at St Audries as well, all easily found. Other than that you can go almost anywhere these days. I know quite a few go to Benidorm if you are after more sun that you get in Eastbourne or Blackpool.
have a look at this link if you do not know of trans events: http://www.northernconcord.org.uk/other-events.htm