can 3 mobile broadband increase their charges mid contact.?

I am a three customer and have been at the wrong end of their charge increases in the past.

If the charges are going up ONLY for the VAT increase in January then you can't cancel your contract, as VAT is beyond their control. However, if the charges are going up for a different reason, then you can cancel your contract once the extra charges are applied, as the law states that a contract cannot be changed to the detriment of the parties signed to that agreement, and an increase in charges is your detriment.

That sounds like legal jargon, but I have used that argument to get out of a number of contracts with three in the past, with some success.

It all hinges on why the charges are being increased. VAT increases are not grounds for cancelling contracts, but things such as increases in line rental, call charges, charging for services that were previously free, are all grounds for cancelling.

Cancellations under these rules would require that you give 30 days notice; but you would be allowed to keep the phone, with no further charges, other than the final month's line rental from when you are in your notice period.

Absolutely not !! if they are going to increase your monthly payment they are breaking your contract agreement. The VAT increase as I am sure you are aware is beyond their control therefore you do have to accept this but not an increase for the service they are providing.

This would mean you can cancel your contract once the change takes place, you will still have to give 30 days notice.

Wow!. No. Surely not :s. A contract can't be altered once the contract has been agreed by both parties. You can cancel a contract but you would have to pay the remaining fees. You could always say your moving house. Put the sim card down the drain and tell them you now live in north korea or something haha :)