One of the tricky points about Baseball in Britain is one can be talking about one of 2 different sports - American Baseball played in the UK or the sport of British Baseball. British Baseball is strongest in South Wales and Merseyside. The Welsh Game is administered by the Welsh Baseball Union and the English by the English Baseball Association, in 1927 the two came together to form the International Baseball Board which administers the rules.
British baseball now has a web presence, so find out more at these sites:
The Welsh Baseball Union generously sent me a copy of the rules, from which I have created a pdf version which can be downloaded HERE.