Vodafone, EE and Lebara are the worst mobile phone providers in the UK, according to a survey by consumer watchdog Which?

Giffgaff was the highest-rated, with a customer satisfaction score of 79 per cent, followed by Asda Mobile (72 per cent) and Tesco Mobile (70 per cent).

Giffgaff is a budget, pay-as-you-go operator which runs on O2’s network. It has no shops or customer service telephone line, but uses online agents to address customer issues.

Lebara, which offers low-cost international calls, came bottom with a customer satisfaction score of 46 per cent, while Vodafone and EE trailed close behind on 49 per cent.

Mobile phone users lose £5.4bn annually, Which? claimed, by being on a contract less than optimally priced for their usage patterns.

Two of the top three mobile providers use O2’s network infrastructure, while four of the bottom five providers use Vodafone’s network.

Vodafone is the most complained about pay-monthly mobile provider, according to Which?, while one in ten EE users rated customer service as poor or very poor.

“We have cut our customer complaints in half over the last year to outperform the industry average", an EE spokesperson said.

"Ofcom’s recent reports have recognised our continued improvement."

The Which? survey asked more than 4,000 people in the UK to rate their provider on qualities such as value for money, ease of contacting and customer service.

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“Major mobile providers are still failing on the basics of customer service”, Which? director of campaigns and communications, Alex Neill, said in a statement.

“Telecoms are an essential part of modern life and so providers need to start delivering for their customers.”

In a separate survey on broadband internet providers, Zen Internet came out on top, scoring more than double that of the worst provider, Talk Talk. BT and EE Broadband were also rated poorly.

"We recognise that the end of last year was a time of great uncertainty for TalkTalk homes", a Talk Talk spokesperson said.

"Levels of customer satisfaction have increased in recent months."

A Lebara spokesperson said: "Whilst we continue to expand, our customers remain at the heart of our business as we also continue to make improvements to our offerings and contact centre capabilities."