Some mobile networks, including BT, EE, Tesco Mobile and Vodafone, have previously sold some mobile phones that can’t be used on other networks unless they are unlocked.

But this is a potentially complicated process which normally costs about £10. Ofcom research found that more than a third of people who decided against switching said having to get their handset unlocked would put them off. Almost half of customers who try to unlock their phone have difficulties doing so.

But the regulator has outlawed this practise. It announced the rule change last year, with it taking effect from today.

Ofcom’s research shows that more than a third of people who decided against switching mobile networks said having to get a handset unlocked put them off changing provider. This means they could be missing out on a better deal. And almost half of customers who try to unlock their phone have difficulties doing so – including long delays or loss of service.

The new Ofcom rules mean mobile companies are now banned from selling locked phones. It says this will make it easier for people to move to a different network with their existing handset, hassle-free.

Any mobile customers who want to change provider can take advantage of the text-to-switch process, where you can get the code you need to switch by sending a free text message.

Other new measures that come into force today include extending rules that limit phone and broadband contracts to a maximum of two years, so they cover bundles. Also, if a customer adds a service to their package, providers will not be able to extend the contract periods of the existing services the customer already has without their consent.

Ofcom says this will help give customers more flexibility to switch package or provider, without being locked into long deals.

The regulator has also strengthened existing requirements on phone and broadband companies to provide blind or vision impaired customers with bills and contract information in accessible formats, such as braille or large print.

It has extended the scope of these rules, so disabled customers can request that any important information about their service – excluding marketing materials – is provided in a format that is reasonably acceptable to meets their needs, and at no extra cost.