27.2% here. Suppose it makes RPI + 3.9% look not so bad after all…
What makes you so sure? Your 27.2% increase is because VM offer fixed discounts, ie £x per month off standard rate. The bigger your discount, the higher the increase is. And this means next year's RPI + 3.9% is going to be calculated as a cash increase and be applied in the same way.
VM currently quote the introductory offer for the Big Bundle at £29.99 a month, and the undiscounted price is £65 a month. From VM's point of view that's not 53.8% discount, that's a fixed £35.01 discount. If the standard rate changes, your underlying price gets increased, and then VM keep taking off your £35.01. So a 13.8% increase - assuming that's the rate VM apply to this bundle - on £65 will be an extra £8.97, when that's applied to the £29.99 bill, what that customer pays is going up by 29.9%. Since VM like to keep standard pricing in round numbers, the actual increase varies a bit on each bundle, but the effect is much the same as outlined here, maybe you are on the Big Bundle. Now see what happens next year:
If we guess RPI is 6.1% between now and early next year, then that's a 10% rise to the basic price. For anybody still "in contract" for the Big Bundle deal by that time, then the maths are as follows:
March 2023: Discounted rate £29.99. New price is (£65.00 x 1.138) - £35.01 = new discounted price £38.96, new standard price £73.97, effective price rise 29.9%
March 2024: Discounted rate now £38.96. New price is (£73.97 x 1.10) - £35.01 = new discounted price £46.36 (new standard price £81.37), effective price rise 19.0%
I suppose 19% is indeed a better increase than 29.9%, on the other hand (a) the 19% is on top of the 29.9%, and (b) at least this year you can leave or renegotiate - due to the new T&Cs next year customers will have to take the increase like it or not.