gap could only occur "if the market and regulatory systems totally fail". The authors argue that if the fair assumption is that power systems are operated to maximise efficiency and minimise costs, then using the amount of OCGT that Hughes suggests, in the way that he suggests, is irrational. Hidden calculations These responses have taken a long time to emerge, but this appears to be because Hughes did not publish his working. Hughes did many of the calculations himself, without showing how his calculations were done, or referencing where his original numbers came from. For instance, his headline-grabbing figure on the inefficiency of wind power is referenced only as "author's calculations" , something we pointed out when the GWPF first released the report. Without being able to get to the bottom of Hughes's assumptions, it is hard for people to understand the full implications of his claims - which arguably isn't helpful when the UK is having to make important choices about its energy future. Updated on 23rd October: Gordon Hughes has posted a short response to Imperial College's criticisms on the GWPF website.