From the BBC listings page:
"The Grey Man is a sweet story of a downtrodden bank clerk, Kevin Dodds who eventually fights back; giving his wife the perfect anniversary present and exacting mild revenge on his tyrannical boss at the same time.Information on the ex-SAS author can be found here on wikipedia.
Written by Andrew Rattenbury based on a 'quick read' by Andy McNab for World Book Day 2007. Daniel Ryan and Olivia Colman play Kevin and Linda Dodds, Christopher Fulford, the uncompromising bank manager and Nitin Ganatra is Gary, Kevin's 'fool' of a best friend. Daisy Donovan and Billy Murray also appear."