By Richard Black
Environment Correspondent, BBC News website
Wave and tidal power can provide a fifth of the UK's electricity needs, according to a new report.
The Carbon Trust, which helps firms develop low-emission technologies, urges the government to increase support for wave and tidal concepts.
They are currently costly ways of generating electricity but the Trust's report says prices will come down.
Investment now could help Britain establish a global lead in these technologies, it says.
In its 18-month research programme the Trust has looked at wave and tidal stream generation, leaving out other approaches to tidal power such as barrages which it describes as "mature".
A barrage on the Rance estuary in northern France has been operating since the 1960s but the concept has been restricted by concerns over cost and local environmental impact.
Wave-based devices generate electricity from movements of the sea surface, whereas tidal stream installations sit on the sea floor and use the regular ebb and flow of tides.
"Wave and tidal stream technologies are at an earlier stage of development than solar and wind which are more mature," said the Carbon Trust's programme engineer, John Callaghan.
"It will cost more than other renewables for the first few hundred megawatts generated, but beyond that there is potential for costs to reduce," he told the BBC News website.
Despite Britain's long shoreline and the vast power contained in its breakers and tides, the Carbon Trust believes only about one fifth of the country's electricity could economically come from the sea.
It says that wave farms could generate 50 terawatt-hours (TWh - one thousand million kilowatt-hours) per year, and tidal stream installations a further 18TWh.
The tidal flow at Strangford Narrows will soon be generating electricity
These figures compare to the current UK total consumption of 350TWh per year.
"You need a good site for wave or tidal energy, but you also need access to the site, you need a grid connection," said John Callaghan.
"There is particular potential in north-west Scotland and south-west England; about half of the total tidal stream resource is in the Pentland Firth [between the Scottish mainland and the Orkney Islands]."
The report says the government should increase support for these incipient technologies and develop "a clear long-term policy framework of support to the sector to give greater investment certainty".
While the Department of Trade and Industry does provide financial incentives, the government's energy review, launched on Monday, barely mentions marine technologies.
Currently, only a handful of wave and tidal stream devices are installed around the UK.
Scotland hosts two prototype wave machines, the Pelamis deep-water system and the Limpet shoreline device, while Marine Current Turbines has been testing a prototype tidal stream concept in Devon and is about to install a commercial device at Strangford Narrows in Northern Ireland.
"We do believe that very quickly we can get down to the same costs as offshore wind," said Marine Current Turbines managing director Martin Wright.
More importantly, he says, assumptions about energy within Britain have undergone a sea-change.
"There has always been an assumption that the price of energy was going to be low - two and a half pence per kWh - and we had to drive downwards towards that price," he told the BBC News website.
He added: "There was no conception we'd be entering a world where energy was short; now it's becoming clear that for the first time in history we are going to become a considerable energy importer, with concentration of fossil fuels in a few hands, such as Russia with natural gas.
"We're now entering a stage where tidal and wave have got to supply 20% of Britain's needs; if we don't, we've got a big problem."
According to the Carbon Trust, the benefits of ramping up investment in marine generation would be considerable, providing not only a reliable source of power, but the chance of dominating a global market in the same way that Danish companies took an early lead in the wind turbine industry.