I'm unconvinced that Bristol (or any other region of the UK, especially those commutable to London) has the critical mass necessary to support one. Perhaps a worthwhile experiment though.
Whether a HN meetup would be successful or not is another story. It'd be entirely down to who would choose to organise it and what they could offer to local HN members.
They used to make everyone introduce themselves at the start, modern HN meetups lack that sense of intimacy :)