Well my lesson was surely learnt. The guppies have gone to live elsewhere and now the betta rules the roost. He seems to get on ok with the platies and swordtail but will have to keep an eye on things for a while until I am sure they get along.
Definitely watch him with the platies and swordtails as well. They might be unscathed so far because they are a bit faster swimmers than guppies. Both of the bettas I got intending to be community fish took to taking chunks out of platy tails quite readily. Needless to say, the bettas live alone now!