I have spoken with OfCom and Orange Mobile Executive Office this lunchtime.
OfCom are clear that Section 9.6 of the Telecoms Act 2003 is applicable to all charges and that a service provider must give the option to terminate. These are the customer's rights in law, regardless of what Orange Terms and Conditions are. As the news story says, this price rise in materially detrimental and customers should have the option to terminate.
Orange Mobile Executive Office responded by claiming that that clause of the Act does not apply to monthly tariffs. They also said that their rise had been 'run by' OfCom. I put this point back to OfCom, who were clear that it does apply (it applies to all parts of a pricing structure) and that they had not been consulted.
I am awaiting the written reply from Orange before taking this up with the Communications and Internet Services Adjudication Scheme (CISAS), who would adjudicate on the matter.
Read it for yourself: Scroll to Section 9.6 of the Telecoms Act 2003 on OfCom website (I cannot post links yet, as new user).
Call OfCom - the more, the better 020 7981 3040.