Operators of historic vessels could be sunk by requirements costing up to £250,000 per boat

Once, thousands of sailing barges plied the Thames estuary. Today, the sight of Will, the largest such vessel still travelling on the waters in London – now converted for pleasure cruises – turns heads.

Passengers on the deck of a giant cruise ship sailing up to Tower Bridge peer and wave at the historic barge below. But Will’s co-owner, Mark Tower, 60, warns that such sights – “absolutely part of the Thames maritime heritage” – could soon be lost.

Under new safety proposals, passengers will be barred on such historic boats unless their owners make costly changes to the design. “It will kill us commercially. And without a business, there’s no boat,” said Tower.

While boat owners agree that safety is paramount, they say the scale of bringing old boats into line with new, under Maritime and Coastguard Agency (MCA) proposals, could close their businesses and lead to skilled jobs – as well as popular passenger boat services – disappearing.

Facebook Twitter Pinterest A crew member at work on Will. Photograph: Martin Godwin/for the Guardian

Most contentious are rules to ensure a vessel’s “survivability”. New boats have compartments to keep them afloat after a collision. More than 600 vessels around Britain could be affected by the proposals, and for many the economics are grim.

The shadow of the Marchioness disaster 30 years ago, when 51 people died after the pleasure steamer sank upon being struck by another boat, still lingers over operations on the Thames.

All operators have absorbed the costs of additional lifeboats and other safety equipment mandated since 1990. But the MCA says that despite major improvements since the Marchioness tragedy, “The reality is that safety gaps in some areas mean the consequences of such an incident have not appreciably changed.”

Sailing barges, featuring flat bottoms for shallow waters, were common on the estuary a century ago. Built in 1925, Will was converted into a mahogany-panelled saloon by P&O and the boat can now be chartered for entertaining.

The unusual interior could be cut in two or disappear under proposed regulations, and that could spell the end for it, said Tower, who has sailed historic boats for decades after growing up watching barges on the river Medway. “There is no National Trust for maritime heritage. To trade with passengers is absolutely vital.”

Further up the river, Colliers Launches has run cruises from Westminster to Hampton Court for 35 years. Danny Collier, 61, and his brother John, 55, show photos of their boat, the Princess Freda, with Dunkirk veterans on board to mark anniversaries of the second world war rescue. Another photograph shows Freda ploughing through choppy Channel waters.

Freda has carried half a million passengers up and down the Thames. Another Collier boat, the Queen Elizabeth, was part of the 2012 diamond jubilee pageant on the river.

The proposals puzzle the brothers, who have operated boats with no major incidents for decades – “and at a time,” said John, “when the Thames was much busier, and London was the busiest port in Europe”.

Both brothers had seven-year apprenticeships on the water, and suggest that knowledge is the most important safety attribute: “It’s knowing what you’re doing, and what everyone else is doing.”

Both boats, and a larger vessel in their fleet of four, would fall foul of rules requiring subdivision below the waterline, in effect wiping out the Freda’s saloon, bar and toilets.

Such radical change would cut capacity from 130 passengers to just 50 and require a huge outlay, said Danny. “Rebuilding for this boat alone would cost £250,000. We’ll go out of business.”

Fred Moore, director of Cruise Loch Lomond, which operates eight boats on the loch, said the MCA proposals had been “terrifying for us” – although he now expects them to be alleviated for the non-tidal waters in which his boats operate.

“If it came into force, we would absolutely struggle. We would not afford to build a fleet of new boats.” His firm has a staff of 45. “That’s a lot of people out of work in a small area,” he said.

Moore, who sits on the committee of the British Marine Passenger Boat Association, said: “In the Scilly Isles, Devon and Cornwall, there are a lot of small operators that would struggle.”

Facebook Twitter Pinterest Mark Tower aboard his boat Will. Photograph: Martin Godwin/The Guardian

There is cross-party opposition to the plans, with the mayor of London, Sadiq Khan, and the city’s Conservatives appealing to Chris Grayling, the transport secretary, to “identify ways to keep everyone safe … without threatening the boats’ viability”.

The MCA said a second consultation on modified proposals would soon launch and regulation could follow in the autumn. A spokeswoman said: “The government does not want to wait for a tragedy before raising the standards of older vessels to enable them to perform adequately in an emergency situation.”

However, she said there could be provisions for exemptions for boats “if the required level of safety has been achieved by other means”.