Both are damn sight quicker than coal from cold... I think CCGT can go from cold and stationary to best effieceny full chat online in an hour or less. OCGT in minutes and CCGT will run in OCGT mode untill hot...
Perhaps National Grid got the forecast just a litle bit wrong and bought energy from the coals station yesterday to give them a chance to start and heat up. Unlike GT you get bugger all from a coal station untill the boilers are boiling...
Noticed last night there was a bit of OCGT running at midnight ish.