EE has been found to offer the fastest download and upload speeds on mobile devices by Ofcom.
The industry watchdog measured mobile broadband performance in Cardiff, Edinburgh, Liverpool, London and Norwich.
Results indicated that EE had the fastest upload speed across all cities at 20Mbps, while Three came second with 12Mbps, followed by Vodafone and O2 (10Mbps for both).
Ofcom tested YouTube streaming performance by loading the trailer for the latest James Bond movie and found it loaded in HD 97 per cent of the time on EE.
The figure for Three was 87 per cent, while Vodafone and O2 came slightly behind at 86 per cent and 85 per cent respectively.
However, Three was found to offer the quickest response time across the five cities, which Ofcom said is important for users of services such as FaceTime and Skype.
Its 44ms put it ahead of EE, which achieved a figure of 56ms, while Vodafone came third with 81ms and O2 ranked fourth with a 92ms delay.