Critics of the BBC's Bodyguard drama claim it is a far-fetched fantasy: a mentally unstable personal protection officer guarding - and bedding - the Home Secretary, in a world where every senior police job is occupied by a woman.

But the former police chief who advised on the show insists that it is entirely plausible, save for a little artistic licence.

David Zinzan is the adviser on Bodyguard and Line of Duty, both written by Jed Mercurio.

Zinzan spent 30 years with Scotland Yard, working in counter-terrorism, homicide, serious and organised crime, and anti-corruption, rising to the rank of commander in the Metropolitan Police. He also served as deputy chief constable of Devon and Cornwall Police. He was assisted on Bodyguard by James Kirkbride, a former personal protection officer.

"Jed Mercurio is really keen that there is a high degree of authenticity in his drama series, but he recognises that there is always a conflict between what would be totally authentic and what would constitute a high-octane crime drama series. My role is to try and help bridge that gap," Zinzan said.