Millions of mobile phone and broadband customers are facing bill increases of as much as 14% in April.

Many customers are facing sudden big rises for their contracts, under a system the regulator says is "unclear and unpredictable", the BBC reports.

Ofcom, which is concerned at the degree of uncertainty that customers are facing, is launching an investigation into mid-contract price hikes.

Companies often set out in contracts that monthly charges will go up in line with general price rises across the economy, as measured by the official inflation figures.

But dramatic rises in inflation over the course of the last year mean customers face much larger price jumps than they have seen in previous years.

For example, BT, which owns phone service provider EE, raises prices by inflation plus 3.9%, which will mean bills rising by 14.4% at the end of the financial year in March. Other firms will impose similar increases.

Firms have said they need to increase prices to cope with rising costs, especially for energy, and to invest in new infrastructure to meet customers' growing demand for data.

Rob Lister, sales and marketing director of Stonehouse-based Lister Unified Communications, said: "The telecoms industry is just like every other industry and the effects of inflation and wages rises are inevitably being seen in price rises to the end user.

"That said, for two such fundamental parts of our lives and our businesses, these still remain incredibly good value.

"Also it needs to be kept in proportion as these rises are typically just a few pounds per month which, compared to the increases we are all seeing in mortgages heating, food, petrol, mortgages etc is a tiny part of monthly costs.

"Most contracts have always covered these price rises, but for so many years it was irrelevant, until now. That said, it is always worth working with reputable companies who retain fair terms and conditions."