Plans for a footbridge soaring high above the waves between the Cornish mainland and the island fortress of Tintagel have caused a storm of protest.

The site’s custodians, English Heritage, say the bridge will help more visitors reach the island and understand its history better.

It is to be created out of two cantilevers that reach across the windswept void from either side but do not quite meet in the middle. Plans for the £4m project have been formally submitted to Cornwall council but there have been objections ranging from the philosophical – is it all about raising money? – to the practical: might not people get a foot stuck in the gap?

In recent months English Heritage has been criticised for turning Tintagel into a “fairytale theme park” focusing more on its legendary associations with King Arthur than its real, fascinating history.

There was an outcry last year after the head of Merlin was carved into a rockface and a statue of a regal figure that most visitors take to be Arthur was helicoptered on to a prominent spot on the island. The bridge scheme is creating more concern.

Bert Biscoe, a Cornwall councillor and Cornish bard, is among those who have now officially objected to the 72-metre-long (236ft) bridge.

Biscoe said the planning application was one of the most important ever to be put before a council in Cornwall and possibly in the UK and should be subject to a planning inquiry.

He argued that one of the key aspects of Tintagel was the separation of the island from the mainland and worried that the bridge may affect the “interactions between sea, rock and buildings”.

Biscoe also expressed concern that an increase in visitors’ footsteps on the island would erode the structures and archaeology.

He said: “English Heritage wishes to provide a footbridge to increase footfall into the heart of the most delicate and important parts of the archaeological legacy. Even without the proposed footbridge, visits to the island number about 200,000 per annum.”

Biscoe argued Tintagel was central to the understanding not of the legend of King Arthur but of early Britain and modern Cornwall. “It is for these reasons that it is a scheduled ancient monument – not because poems and operas assert that Tintagel is Camelot. Already, we have seen how such commercially driven mismanagement is detracting from the integral truth of Tintagel.”

The campaign group Kernow Matters also objected. It said Tintagel was being turned from a historic site to a “cash cow theme park”, adding: “English Heritage would be first to object if this was attempted on someone else’s historic site.”

For hundreds of years – since a narrow natural land bridge that used to reach out to the rocky headland on which the castle sat crumbled into the Atlantic – tourists, poets, historians and Arthurian enthusiasts have had to scramble up and down hundreds of steps and across a modest wooden bridge to visit the island. The challenging terrain means many simply cannot get there.

But even people who work at Tintagel are expressing worries about the new project. One member of staff has written to Cornwall council expressing concerns over the bridge’s viability.

She said: “Having spoken to countless visitors about the proposed bridge, I must point out that many have said that nothing would get them across, including those not afraid of heights.” The staff member added that she thought the bridge would have to be closed in high winds, which are not uncommon on the rugged north Cornwall coast.

English Heritage insists the bridge will enhance the site. On the practical side it said the gap between the two halves of the bridge was was only about 4.5cm wide so would not be hazardous. The current stairs would remain in place for anyone who could not cross the bridge. It said the bridge would close in high winds – but the site already has to close if it is very breezy, and indeed was shut on Friday.

It said everything it was doing at Tintagel was about reflecting the site’s importance and it put huge effort into explaining what really did happen there and the legends that swirl around it. The bridge will help visitors grasp that the mainland and “island” (or promontory as EH is now terming it) were once connected.

English Heritage argues that the bridge will not create extra pressure but will help manage the current strain. It also pointed out it had consulted with the Cornwall design review panel, which studies major projects for the council. It said it was “generally very supportive” of the scheme.

English Heritage’s head of operations in Cornwall, Georgia Butters, said: “We welcome all feedback as it is important that we get this right. Over the past year, we’ve been consulting with – and listening to – the public and interested parties.

“Above all, the footbridge is designed to complement, not compete with, the surrounding spectacular landscape.”