Thanks for the alert guys, just been looking into it. The site has flood protection as a protection against DoS attacks on the server and will only allow a certain number of connections to the database at any one time.
From what I can see the (suspected) IP is in the UK which is kind of strange that anyone would be making a deliberate attack from their own BT connection. I'm going to for now assume that someone's PC had a hissy and opened a zillion windows.
Co-incidentally Ive noticed from the logs that it also seemed to happen at about the same time that google did its trawl. Ive noticed before that anything up to 30 or so google bots can sometimes arrive all together, will keep an eye on things and hope that this is a one off.