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There is a clause to that effect

H Changing this agreement

We and/or Virgin Media Payments may at any time improve, modify, amend or alter the terms of this agreement and/or the services and their content if:

• there is any change or amendment to any law or regulation which applies to us or Virgin Media Payments or the services we provide to you;

• we decide that the services should be altered for reasons of quality of service or otherwise for the benefit of our customers or, in our reasonable opinion, it is necessary to do so;

• for security, technical or operational reasons;

• if the changes or additions are minor and do not affect you significantly or we wish to have all our customers on the same terms and conditions;

or

• in all other events, where we reasonably determine that any modification to our system or change in our trading, operating or business practices or policy is necessary to maintain or improve the services which we provide to you.

However, you will have the right to cancel the affected services or end this agreement if the changes are significant, as described in paragraph J3


J Ending this agreement

3. If:
we and/or Virgin Media Payments increase our charges under this agreement;
we make significant changes to the services so the services you are entitled to receive in return for the charges you pay are significantly altered or reduced; or
we and/or Virgin Media Payments make significant changes to the terms and conditions of this agreement (including the other legal stuff),
you may cancel those services affected without penalty by giving us at least 30 days' notice in writing.

I would argue that because customers are not notified of changes to T&Cs (other than changes in pricing) then it is impossible to know whether any change is 'significant' and warrants cancellation of the service.