Lobbying by Britain looks set to have secured a key concession in EU plans to cut power station emissions due to be voted through the European Parliament this week.
The extra time will be much-needed breathing space as Britain struggles to avoid an "energy gap" as polluting coal-fired plants are closed down by existing EU rules on pollutants such as sulphur dioxide at the end of 2014.
After months of discussion, the European Parliament's Environment Committee is expected to agree to shift the deadline for the next stage of cuts from the end of 2015 to mid-2019.
The original plan for a 2015 deadline is part of the integrated pollution prevention and control (IPPC) directive which will follow on from the large combustion plant directive (LCPD). But it was opposed strongly by the European Council of member states, which proposed a 2020 deadline to give generators more time to upgrade emissions reduction equipment.
Under the LCPD, power plants must cut emissions of proscribed gases by 94 per cent. Any unable to do so may run for a further 20,000 hours or until the end of 2014, and must then be scrapped. Some 10 gigawatts (GW) of Britain's generating capacity are due to be retired as a result.
The new IPPC directive increases the cap on noxious emissions to 96 per cent. But before the directive becomes law it must be agreed between the European Parliament and the Council of member states. And only once parliament has finalised its position this week can the compromise with the Council's 2020 deadline be negotiated.
Holger Krahmer, the MEP who is the rapporteur for the IPPC – charged with corralling an agreed position from the Parliament – is confident that the extension until June 2019 will be voted through tomorrow.
"The conclusion is a little bit speculative at this stage, but it is fairly certain that a big majority of the environment committee with vote for the  compromise," said Mr Krahmer. "The most likely outcome is that the deadline will be extended by four years, although I regret it because I think the member states had enough time to invest."
The loudest calls for extra time from the European Council came from Britain. "The UK was the loudest and strongest lobbier," said Mr Krahmer. "The British pressure on this was very, very high."
The four-year extension will be of considerable benefit to electricity producers already reeling from the high cost of fitting desulphurisation equipment to meet the 94 per cent target, according to Ian Parrett, a market analyst at energy consultancy Inenco.
"The old timescale for the second phase wasn't really possible," said Mr Parrett. "The generators have already invested so much to get to the first target that it just wasn't economically realistic to upgrade all the equipment so soon."
But even with the hard-fought concessions – which could be signed into law as early as the summer – Britain's energy supplies over the middle of the decade will be tight. The first nuclear power stations are not scheduled to be up and running before 2017, even if the highly rigorous construction timetable is met without a hitch. And plans for massive increases in the amount of off-shore wind power are also both financially and logistically ambitious.
Sceptics warn that Britain may be forced to throw up gas-fired power stations, which are quicker and cheaper to build than either nuclear or renewable generation, leaving the country over-reliant on foreign suppliers, particularly Russia.
There are also questions about whether the planning process would enable replacements to be built in time, if at all. Scottish Power plans to convert its Cockenzie coal-fired power station to a new gas plant were vetoed by East Lothian Council last week, moved by complaints from local residents about the scheme's impact on nearby communities.