Here's a quote from UK energy minister in the press release:

Malcolm Wicks, Energy Minister, said: "This is a welcome move by Centrica which is investing to secure the future energy needs of UK consumers. Langage will contribute towards the UK's security of supply as new and more efficient power stations are needed in the coming years to replace existing plant."

Elsewhere in the press release is the commissioning date for new power station, 2008/09.  Here are a few of my assumptions: Norwegian gas from Ormen Lange will come online during 2007, will deliver 20 bcm pa i.e. some 20% of current gas demand and N Sea gas is declining at 8%pa from current output of 90 bcm pa.  On this basis Ormen Lange will only 'fill the gap' between 2007 and 2010 by which time UK supply position will be back to what is was immediately before Ormen Lange startup, hence current big LNG program.

In effect only LNG can supply the incremental gas required by this new power station....and LNG is anything but cheap.  Furthermore I can't share the minister's confidence regarding 'security of supply' as continual supply of LNG depends on reliability of supplies from such places as Qatar (where they have a current moratorium on new LNG contracts due to questions regarding the North field). If / when new LNG contracts are let by Qatar UK will be only one of a sizeable (and growing) number of nations who will be competing for LNG supplies and the tankers to transport same.

In summary the new plant is quick and relatively cheap to construct and is cleaner than coal plants, for example. Whether the gas supply to fuel it will be dependable and cheap is another matter entirely.