I found out that to launch a balloon you need to contact the UK CAA and they will approve your launch after you have completed form DAP1919.
DAP1919
https://www.caa.co.uk/application.aspx?catid=33&pagetype=65&appid=11&mode=form&id=4409
On the day you need to contact the nearest airfield and liaise with them on an appropriate launch time.
When you get permission to launch you will be given this document
2011060312Perm10MetBalloonReleaseCaderIdrisWelshpool
click to open
