Unfair Terms in Consumer Contracts (UTCC) Legislation
I left Orange a few years ago when they hiked up the price of broadband - and they tried to charge a disconnection fee when I refused to accept the price hike.
However, the Unfair Terms in Consumer Contracts (UTCC) regulations mean that if a company has standard contracts that the customer cannot influence, and some of the terms and conditions are measurably unfair to the customer and biased towards the company - then those particular terms cannot legally be enforced (though all other T&C still apply).
In my case I sent a letter to Chief Executive of Orange stating that they cannot simultaneously raise the contract price, and also charge me for leaving the contract as this would be unfair under UTCC. I expected them to either honor my original contract at the original price, or allow me to leave the contract without paying an exit fee.
Orange subsequently wrote back and whilst not admiting they were in the wrong - offered as a 'goodwill gesture' to cancel the account charges.
So if Orange try to apply exit fees for you to leave then wave the UTCC regulations at them!
PS - Writing to any companies Chief Executive usually gets results far quicker than dealing with the accounts department :)