A trip to the Norfolk seaside is costing people more than just the price of chips and a Mr Whippy - with beachgoers reporting shock additions to their phone bills.
Poor mobile coverage along the county's coast is causing handsets to latch onto signals from passing ships rather than UK masts.
This tricks the networks into thinking the phones are out at sea and automatically switches them to 'Maritime Mode', connecting them to satellites via the ships.
A text from iD Mobile received while at Sheringham beach (Image: Supplied)
At this point, customers are hit with roaming charges which apply to calls, texts and data.
Charges vary depending on the network, but calls can cost around £5 per minute, while data can run at £10 per megabyte, meaning a few minutes of web browsing or video streaming could cost tens of pounds.
Locals and holidaymakers have been reporting such issues over the summer while visiting several beaches, including Sheringham and Mundesley, as well as Cley Harbour.
They are calling on the phone companies and politicians to do more to address the problem.
Mike Costello (Image: Mike Costello)
However, the firms say that the ships have a part to play too because vessels are supposed to disable their roaming capabilities when passing near the coast.
LOCAL FRUSTRATION
Vodafone customer Denise Revell, from Mundesley, said she was billed for roaming while simply sitting on the beach.
One holidaymaker was hit with a £10.74 charge from iD Mobile while visiting Sheringham for the day, calling it "unacceptable".
Another received a roaming warning message while at Cley Harbour.
A text received by Mr Costello at Mundesley Beach (Image: Supplied) She said: "I was very surprised to receive a text from iD Mobile which said I appeared to be travelling by ship.
"I quickly put my phone on aeroplane mode to avoid any charges, which were nothing short of extortionate."
Retiree Mike Costello says the issue seemed to be particularly acute in Mundesley, where he lives.
"A lot of people probably don't even notice it happens as it swaps across and swaps back again," he said.
Mundesley Beach (Image: Newsquest)
"Unless you're vigilant about checking your bills, you don't notice.
"The phone signals around here are a bigger issue.
"If we had better coverage on land, it wouldn't be searching for signals at sea in the first place.
"I'm with EE and my wife's on Vodafone. It seems to happen more with her phone so she's now turned roaming off completely to stop it.
"It affects local businesses too, because their card readers don't work."
Phone signal coverage in north Norfolk is often poor (Image: Newsquest)
Mr Costello has now purchased a Starlink Mini satellite unit for reliable Wi-Fi at home.
He added: "It works brilliantly, but of course it's something I shouldn't have had to buy.
"You'd think in this day and age, having good mobile coverage would be a priority."
Ed Maxfield, county councillor for Mundesley, said: "It's all very well for the providers to insist on their customers contacting the provider to report the issue, but this is a systems problem that they ought to be sorting out themselves."
Norfolk County Councillor for Mundesley, Ed Maxfield (Image: Supplied by Ed Maxfield)
COASTAL 'NOTSPOTS'
Previous surveys have identified several areas of the coast with particularly poor mobile phone coverage.
A Norfolk County Council project involved fitting devices to bin lorries to track signal strength across the counties to locate 'notspots'.
Communities worst affected include seaside ones such as Happisburgh and Eccles on Sea.
Campaigners warn that weak or absent signals leave vulnerable residents feeling unsafe, as they cannot call for help in an emergency.
EE mobile phone coverage in Norfolk - red is 'poor', yellow is 'essential', light green is 'acceptable' and dark green is 'good' (Image: NNDC/ Streetwave) Three mobile phone coverage in Norfolk - red is 'poor', yellow is 'essential', light green is 'acceptable' and dark green is 'good' (Image: NNDC/ Streetwave)
NETWORKS RESPOND
VodafoneThree said it had not yet received customer complaints in Norfolk but urged anyone affected to come forward so they could investigate further.
A spokesman said: "Inadvertent Roaming can happen when you live or travel close to a coastline - where you can connect to a maritime network - or an international border."
O2 said that maritime operators were responsible for disabling roaming near the coast but promised refunds "as a gesture of goodwill" if customers were billed incorrectly.
A spokesman added "To go further and support our customers, we took the decision to switch off data roaming when connected to maritime services to prevent inadvertent charges and unexpectedly high bills."
EE mobile phone coverage in Norfolk - red is 'poor', yellow is 'essential', light green is 'acceptable' and dark green is 'good' (Image: NNDC/ Streetwave) O2 mobile phone coverage in Norfolk - red is 'poor', yellow is 'essential', light green is 'acceptable' and dark green is 'good' (Image: NNDC/ Streetwave)
EE said handsets are designed to connect to the strongest available signal but stressed that users can turn roaming off in their settings, apply a roaming bar through the EE app, or ask customer service to do it for them.
"In the event of any customers being charged incorrectly, we would refund them where appropriate," a spokesman added.
HOW TO AVOID ROAMING CHARGES
* Turn off roaming in your phone settings or mobile account.
* Apply a bill cap (as low as £0) to stop unexpected out-of-plan charges.
* Switch to airplane mode or use Wi-Fi only when near the coast.
* Contact your provider if you have been billed - most will refund.