Analysis by consumer group Which? found some providers bump up bills by as much 60 per cent for loyal customers who don’t take action at the end of their initial minimum contract.

Natalie Hitchins, head of home products and services at Which?, said: “While there is nothing wrong with staying with your supplier if you are happy with your service, it is worth noting that without doing anything at the end of the minimum term you could end up paying over the odds. You might save yourself a lot of money by haggling.”

The worst offenders

Which? analysed current entry-level fibre broadband and phone deals across 12 of the biggest broadband providers on the market.

Virgin was the worst for penalising loyal customers. Anyone signing up to the M50 Virgin Media tariff face bill hikes of £16 a month or £192 a year at the end of their initial 12-month contract.

The Post Office was another culprit. Its entry-level fibre broadband package for new customers starts at £24 a month but rises to £37 for anyone who chooses to stay past the minimum term and doesn’t renegotiate a lower price.

John Lewis also came out badly. Its Broadband Fibre deal goes up by 38 per cent once the 12-month period is over, from £27.50 to £38.

Utility Warehouse and Zen internet were the only two suppliers to keep their prices the same for new customers and those who stay put, with no hike after the minimum term.

Keep an eye on the date

While providers are upfront about the standard cost after the initial offer period, it is easy for customers to lose track of when their contract is coming to an end. That’s why it’s important that they keep track of the date they need to renegotiate their deal, or switch.

From February, TV, mobile and home phone providers will have to notify customers when their contract is coming to an end and inform them of their best deals available.

However, providers will only show their own deals and customers will still need to shop around to get a good view of the whole market.

Last month, the biggest broadband providers signed up to Ofcom’s fairness commitments, promising to help customers find the best and most suitable deals for them.

They also pledged to make sure that customers are kept well informed and well-equipped to make good decisions about their broadband as well as their pay-TV and mobile contracts.

The regulator said it will continue to monitor companies closely and will intervene when it feels firms are falling short of their commitments to customers.

Hitchins said: “These findings continue to show it is imperative that broadband customers who are out of contract either contact their supplier to secure a good deal or shop around and look to switch elsewhere.”