And perhaps to spell out what this means for you:
1) In April this year your price goes up, by well above inflation because VM are applying an above-inflation increase to the standard price, and then adding that increase to your discounted bill. So your month on month increase is probably in the 20-30% range, depending on how good a discount you have. The better the discount, the higher the proportionate price rise.
2) In the next 30 days you can reject this increase, and cancel without penalty, and as soon as you do that your 30 days notice period starts to tick. Obviously you'll need to find another ISP who aren't planning the same thing, or can offer a fixed price, or better value new customer deal. I've recently got a 12 month fixed price broadband deal with a smaller ISP known for their customer service, but you need to do your research on those and what their offer is, and allow for both any special offers, discounts and new connection charges.
3) You can phone VM to reject the price rise and cancel, but with the actual intention to play the retentions game and agree a new 18 month contract and discount. That may result in a good deal, it may not. As the other ISPs who VM benchmark against are all doing similar things, your leeway may be limited. I'm told there's an automated offer been put up on VM systems where you can get a modest additional discount for six months without changing your contract, although it will still mean an increase in April.
4) If you choose to stick with VM and their April increase (with or without any automated discount offer), then in September your existing discount ends and you'll need to cancel or speak to retentions at that time, otherwise you'll roll on to the full fat and heavily inflated tariff.
5) Regardless of any new deal you agree with VM, come this time next year, VM are changing their terms so they will be able to apply their disgraceful, grasping RPI + 3.9% formula (again on the undiscounted rate) without you having any right to cancel, but with you still tied in for the remainder of any fixed term.
I decided before this latest announcement that I'd had enough of VM's price rises, poor service, and the sinking feeling whenever I needed to contact them, so I've taken my business elsewhere. I'm not using the VM connection now, but it is still live for a further nine days, then no more VM forever.