My review -
The government believes it's impossible for London to experience a blackout. Each generating station has another ready to take up the slack in the case of failure. They reckoned without a group of idealistic eco-warriors who are determined to shut off the city's power supplies to show Londoners they can cope without profligate use of electricity. What they don't know, but it becomes increasingly obvious that the higher powers in the land do, is what waits underground ready to emerge when the lights go out. The goverment's Dark Protocol is engaged and found wanting.
This is an intriguing premise and leads to exciting scenes as different small groups try to fight for their existence through the longest night of their lives. Even the Prime Minister’s family isn't immune to those things which inhabit the London Dark. I think the author has great strengths as a horror writer and I’d happily read more from him in this genre. Highly recommended.