If you've never had a speculative look at where to go for the weekend from London using Skyscanner, you might be surprised to learn that Birmingham and Bristol are frequently options, sometimes for virtually nothing self-connecting with FR via DUB and other times for about £400 using KLM via AMS.
There was a story in our local press a while back about a student travelling back to Uni in Essex from Sheffield area via Berlin as including the buses it was cheaper than the train. So people will do it, if they save a bit.