Customers who have reached the end of their mobile phone contract should have their phones unlocked from the network for free, says consumer group Which?

It believes that keeping phones locked prevents customer finding a better deal by switching providers.

Pay-as-you-go mobiles should not be locked at all, it said.

One mobile operator said its phones were locked to prevent fraudulent activity.

When a mobile phone is purchased from an operator it is locked to that particular network until the contract expires or until the customer requests it is unlocked. This means the phone will not work if the Sim card from another network is used in the device.

Which? said that companies should also be forced to tell customers which is the best deal for them once their current contract has expired.

"Mobile phones are an essential part of daily life for many people and consumers shouldn't be locked into contracts that do not suit their usage," said Which? executive director Richard Lloyd.

'We want to send a message to mobile phone companies that they should help customers get a better deal by alerting people that their contracts are about to end and by unlocking handsets for free."

BBC News