Small mobile network providers, some of who only charge £5 a month, were more reliable than their big four rivals in a survey of more than 4,000 customers .

EE, O2, Three and Vodafone were ranked worse than their smaller rivals including Smarty, Voxi and Talkmobile by Which? with Smarty scoring 82% for its rolling sim-only deals and praise for its value for money offering. Rolling monthly sim-only contracts for the big four networks start from £19, whereas the top performing smaller firms were charging around £5 and including more data.

Which? said that O2 customers were seeing their SIM-only contracts rise £1.80 while EE’s were increasing £1.50, with Three up £1 to £1.50; and £1 to £1.80 for Vodafone customers.

Natalie Hitchin head of home products at services at Which? said that smaller providers were offering better customer service, more reliable connections and cheaper Sim-only deals without any mid-contract price hikes – giving their customers more certainty about what their monthly bill will look like.

Smarty topped the table while Voxi and Talkmobile followed just behind with scores of 81% and 80%, and neither imposes mid-contract price hikes said Which?

The worst provider was Three which socred 63% while O2 and Vodafone scored 68% and 69% respectively. 

Which? noted that O2’s average ratings had dropped and that Vodafone was criticised for its network reliability and incentives and rewards offered. 

EE managed a rating of 71% and customers were largely happy with its download speeds, although its incentives and value for money when roaming were rated poorly.