Alpari will give you
MT4 to play with and have left me completely alone.
Capital Spreads have a demo Spread betting account as do Barclays Stockbrokers but their platform is stone age.
As said above (or below) do not give your normal email or phone number to them. I was pestered by a very earnest and aggressive American woman on my car phone which I check once a week, for messages. Since she always rang in the middle of the night (in the UK, she never got me before she gave up, so clever, earning a bundle, but not savvy enough to figure out the time difference.