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The stations are intended to plug the gap left by the decommissioning of nuclear and coal power stations over the next 10 years.

Each of the plants will cost about £750m, and together they will produces nine gigawatts of power. Britain is expected to have a shortfall of 15-20 GW - about a quarter of the country's present generating capacity - by 2016.

Shaun Taylor, project director for F+A's energy unit, said: "It makes sense because of the speed they can be built. It can take seven years just to start putting holes in the ground on a nuclear plant, whereas you can throw up a gas station in about three years."

Taylor declined to name the client, although it is understood that the private sector will develop the six stations. Consultants specialising in the power industry believe only Powergen or Npower would be able to take on such a large project.

Taylor added that the six stations would be spread across the UK.

Separately, Powergen has recently submitted planning applications to build gas power stations at Drakelow in Derbyshire and on the Isle of Grain in Kent.

ºÃÉ«ÏÈÉúTV of F+A's appointment comes amid renewed pressure on the government to bridge the energy gap.

It can take seven years to start on site with nuclear, whereas you can throw up a CCGT in about three years

Shaun Taylor, Franklin + Andrews

The House of Commons' Environmental Audit Committee last month launched a report backing the construction of a new generation of gas-fired power stations in the next 10 years, alongside renewable energy sources such as wind turbines.

The report added that another "dash for gas" could bring significant carbon savings, as modern combined cycle gas turbine gas stations would be much more carbon-efficient than the coal-fired stations they would partly replace.

Others have pointed out that carbon sequestration would need to be used to make the stations truly green. Sequestration involves capturing carbon dioxide and other greenhouse gases at the point of emission and storing them.

Nigel Adcock, managing director of Gleeds Energy, said: "Gas-fired stations would fill the gap but seem to be counterproductive to the carbon emissions targets - you've got to address the environmental issue."

Clean-coal power is also making a comeback as generators look to replace capacity that is being closed.

Npower recently revealed plans to build a new power station using the technology at Tilbury, on the Thames estuary. Eon, which owns Powergen, is looking at options to build a clean-coal station in Lincolnshire.