Ranger Nick Dunnett says lime present in the walls of Tattershall Castle can damage newts' skin.

Is this Britain’s most unusual job? National Trust ranger Nick Dunnett spends his days combing the cellars of Lincolnshire’s Tattershall Castle looking for a protected species likened to a “mini dinosaur”.

His target in the 15th Century attraction near Sleaford is the great crested newt.

A very large breeding population can be found in the moat and surrounding land.