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Full or partial mobile signal 'not-spots' affects 70% of firms, according to the study by the British Chambers of Commerce (BCC).
But the proportion of companies based in rural areas which report such issues (91%) is considerably higher than those in inner cities (56%).
'Not-spots' are areas of no mobile coverage by any operator, while 'partial not-spots' have some coverage but not from all networks.
See also: Rural 'not-spots' unacceptable, warn MPs
The survey of 1,465 businesses also show that 29% of firms have unreliable mobile internet connections, with the figure rising to 54% in rural areas.
It found that a considerable proportion of UK businesses are not accessing the highest connection speed, with only 42% of businesses reporting a 4G connection.
Inner city firms (54%) are more likely to have 4G than those based in rural areas (25%)
Some 6% of companies said they still typically obtain a 2G connection and 25% a 3G connection.
Big businesses are more likely to report 4G connections (57% of businesses with more than 500 employees) than their smaller counterparts (41% with 1-4 employees)
BCC director general Adam Marshall said: "All across the country businesspeople complain about patchy mobile coverage and unreliable internet connections in their local areas.
"Time and again, I hear from frustrated businesspeople who can't use their mobiles or access the internet when they need to."
Dr Marshall said these were basic requirements for companies to work on the move, trade online, and connect with customers and suppliers.
"Rural businesses are particularly affected by poor mobile coverage and connectivity, but our research shows that 'not-spots' are prevalent across the UK.
"It's incredible to hear that in this day and age there are even places in the City of London where businesses can't get reliable coverage.
"Some of the solutions are obvious. Relaxing planning laws to allow for taller masts would be a quick win for the next government to help improve mobile coverage.
The BCC is calling on telecoms regulator Ofcom must do more to hold providers to account for the services advertised to business customers.
It is also demanding remedies that are as strong for business users as they are for individual consumers.
Ofcom rules stated that virtually all UK premises must receive 4G signal by the end of the year but the survey results suggested that the target was a long way off.
"It's clear that the UK is lagging in the delivery of access to a world-class digital infrastructure.
While there have been welcome announcements to roll out 5G in the future, it's clear that getting all businesses access to 4G first remains a top priority."
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