This is exactly the issue that all Virgin customers, myself included, are facing where the network is not open access to other retailers. SIRO and openeir sell to most commercial retail operators, and therefore you can easily switch every year with no loss in service. As far as I know Sky have recently signed up with SIRO, so anyone on SIRO can switch from Vodafone to Sky (and others) just by making the phone call. Because Virgin's network is only available to Virgin, we all have to endure this annual increases of in excess of 7% for the last few years.
Love them or hate them - the sooner openeir roll out their urban FTTH programme the happier I will be. I will gladly say goodbye to Virgin and their annual price increase. At least, if other operators do it, I can immediately switch to someone else.
Just checked the companies currently using SIRO (in the interest of fairness)
Digiweb, Sky, Vodafone, Airwire, Carnore broadband, Kerry broadband, Rocket broadband, Westnet, Pure telecom, Nova broadband