The consumer champion found that while rural Scotland and Wales still have Britain’s lowest levels of mobile coverage, many areas that include large towns and cities are also poorly served when it comes to receiving comprehensive 4G mobile coverage.

The research found that parts of Sheffield, Essex, Brighton, Cardiff, Milton Keynes and Leeds were among areas that did not receive mobile signal from all four major operators.

Which? analysed Ofcom’s Connected Nations data to look at the whole of the UK and see how many areas have 4G mobile coverage from all four operators.

The research comes amid discussions between the government and mobile operators about how to boost mobile broadband access in poorly-served areas and ensure the government meets its target of extending 4G coverage to 95 per cent of the country by 2022.

Currently, only 67 per cent of the UK’s geographical area has 4G coverage from all four operators, while 8 per cent has no 4G mobile coverage at all.

Overall, the Which? study found that in 524 out of 650 (80 per cent) UK parliamentary constituencies 4G coverage is not available from all four operators in the whole constituency.

The most poorly-served city-based constituencies – each with less than 80 per cent of the constituency receiving coverage from all four operators – were Rochford and Southend in Essex, South West Devon, and Romsey and Southampton North in Hampshire.

Among the worst affected town-based constituencies for mobile coverage – with less than 60 per cent of the constituency receiving 4G coverage from all four operators – were Clwyd West in Wales, Barrow and Furness in Cumbria, Ribble Valley in Lancashire, and Scarborough and Whitby in North Yorkshire.

Which? found that only three constituencies in Scotland had complete 4G coverage from all four operators – Aberdeen North, Glasgow North West and Glasgow South West.

In Wales, only the constituency of Central Cardiff had 100 per cent 4G coverage from all four operators. While in Northern Ireland not a single constituency area had 4G coverage from all four operators. In England, a quarter (23 per cent) of constituencies have 4G coverage from all four operators.

Caroline Normand, Which? director of advocacy, said: “Millions of people are finding it difficult to get a reliable mobile connection and risk missing out on digital services we increasingly rely on like online banking, maps and NHS information – while some even struggle to receive important calls and messages.

“To tackle this unacceptable and widening digital divide, the government must act now to connect the UK with truly comprehensive mobile and broadband by swiftly putting in place a plan to give communities the infrastructure they need.”