T-Mobile UK has announced that the price of all mobile contracts taken out before February 1st this year will rise by 3.7 percent on May 9th, meaning that long-standing customers will see a monthly increase of about £1 on their bills. The company is able to increase its charges due to a clause in customers' contracts that allows its prices to follow the British Retail Price Index (RPI), a standard measure of inflation. Users who signed up since February 1st and those on The Full Monty or You Fix plans are unaffected.

T-Mobile's not the first to do this: its partner in the Everything Everywhere merger Orange made a similar move earlier this year, and any increases in VAT have also been passed on to the consumer by UK carriers. However, it's bound to come as a surprise to some users that the price they pay isn't the one that they signed up for.