Used IDealing.com for my self select ISA over 3 years never had any problems ,always managed to get good prices ,regularly well within the spread.Can recommend it.
Just to add to my post above, had a limit order in with ComDirect which didn't trigger when it should have - contacted them next day and they bought and credited my acc with the difference - no fuss, just put it right. Exactly what I need.
I agree with Kaytom1, I have used idealing for nearly a year now and am very happy with their overall pricing policy+service.
At 1st i had reservations that they were internet only but if you are unable to deal online (for order size for example reasons) they do provide an emergency phone number to use.