The short answer is “yes”. You can, technically, leave at any point you like, although if you leave/cancel whilst you’re in-contract, you will incur cease charges. These include the price for turning off your service, as well as the total cost of the remaining months you would have been in-contract with your ISP for.

The most cost-effective thing to do is wait for your contract to end, so that you may freely search for a new ISP.

This excellent Ofcom article details how to find out your contract status for every major UK ISP (to see how long your Ballscoigne contract is, please call 0330 043 2568).