The UK’s biggest mobile providers have been outperformed by smaller rivals in an annual customer service survey by watchdog Which?

Three, O2 and Lycamobile were the lowest performing networks in the survey of more than 5,000 mobile users, receiving customer scores of 65%, 67% and 68% respectively.

Three received a two-star rating in every category including network reliability and technical support, the consumer group found.

O2 received just two stars for value for money and customer service, shortly after it increased its annual price rises from £1.80 to £2.50 a month for all customers.

Lycamobile received four stars for value for money but two stars in every other category.

EE and Vodafone achieved scores of 74% and 72% respectively, although Which? described them as “stuck in the middle to lower reaches of the table”.

Talkmobile topped the rankings with a customer score of 83% followed by Tesco Mobile on 81%, with both impressing customers with their network reliability, customer service and value for money.

Other top-rated networks included Giffgaff and Smarty, which both received a score of 79%, driven by their flexibility and affordable Sim-only deals.

Lebara and 1pMobile both achieved a score of 78%, with customers praising 1pMobile’s network reliability and value for money and Lebara earning five stars for value for money.

According to the survey, respondents using one of the ‘big four’ – EE, O2, Three and Vodafone – paid an average of £16 for a Sim-only contract, compared with just £9 on smaller networks.

For contracts including a phone, users paid an average £40 with the ‘big four’ compared with £28 with smaller providers.

Many smaller firms use the infrastructure of the ‘big four’, meaning customers often receive the same signal and coverage.

Which? head of home products and services, Natalie Hitchins, said: “Our latest research shows that smaller providers are consistently outshining the industry’s largest mobile firms by offering better customer service and far cheaper deals.

“Many top-rated challengers avoid mid-contract price hikes, offering households struggling with the cost of living much-needed certainty.

“Any customers nearing the end of their contract who are unhappy with their service, or simply looking to save money, should not hesitate to vote with their feet and move to a provider that actually delivers on value.”