People in Cornwall face a wait of up to 18 months to register with an NHS dentist amid growing concerns that health services in England’s poorest county are at breaking point.

Cornwall has a backlog of more than 14,000 people who want to register with an NHS dentist. Some residents must travel more than 70 miles to find one of the few practices in neighbouring Devon that are still taking on patients.

Practitioners said a shortage of funds was mostly to blame for the lack of NHS dental services in Cornwall and across the UK, along with the impact of the Brexit vote.

The British Dental Association, which represents dental practitioners, said: “A fifth of NHS dental services in England are being delivered by dentists who trained in the EU and overseas. The choice not to offer them any kind of guarantees ahead of Brexit negotiations raises real questions about the sustainability of this service.”

It added that the challenges of providing quality care, necessary investment and coverage for vulnerable patients “require more than a bargain-basement funding model”.

A spokeswoman for NHS England said: “There are no practices able to offer immediate access to a dentist in Cornwall for a routine appointment and we have a waiting list of patients. In some areas, the length of wait may be as long as 12 to 18 months.”

Dentists have blamed NHS quotas for blocking new registrations. The quotas put a limit on “the level of contracted activity that is purchased from practices by the NHS”, which is defined by “the number and complexity of courses of NHS treatment that each practice is commissioned to provide in any 12-month period”.

The NHS spokeswoman said there were moves to increase quotas for dentists in the south-west, but a shortage of practices made it hard to make more treatment hours available. She said: “Demand is clearly rising, though the proportion of people who’ve seen an NHS dentist in the past two years is still well above the regional average and we continue to place hundreds of people with practices each month.”

She urged anyone having difficulty in Devon and Cornwall to call a helpline. But callers to the helpline last week were told no dentists were available and it was likely they would need to wait 18 months for a place.

According to the NHS Choices website, a practice in Redruth was taking new patients, but when the practice was contacted it said the website was out of date and it would only begin registering some patients again in July.

In 2015 a study by the consumer watchdog Which? found that three in 10 NHS dental practices advertising availability could not take on new patients. Nationally there are 7,500 dental practices that provide NHS services, but only 4,500 of them were advertising as being able to see NHS patients. Of the 500 practices contacted by Which?, 30% turned out to be full.

Richard Lloyd, the former director of Which?, said: “It’s disgraceful that so many people can’t access the local dental service they need to stay healthy, and woefully shortsighted if the overstretched NHS then has to pay for expensive emergency treatment instead.

“What makes this even worse is that ministers and NHS chiefs have known for years that dentists often say they are accepting new NHS patients, when in practice they are not, and that people forced into private dental care are often given very poor information about their treatment plan and its costs.

“Local Healthwatch campaigners, who raised the alarm about the growing crisis in Cornwall in 2014, should be given strengthened powers and more resources to hold the NHS to account when it puts people’s health at risk like this.”