Here Be Evil by Michael Woodhams

Separate, brutal murders committed on London’s Hampstead Heath by a single killer, are unusual in that the DNA found on the bodies is of a type unknown to science. Paul Triger, head of the Ministry Of Defense’s Section ‘S’ is called to investigate. Together with MI5 and MI6, he and his team uncover evidence that forces deep within the fabric of the UK’s political and social order threaten the governance and very existence of the British way of life. Who are these forces? Where are they from and what is their ultimate goal?
Investigations through London and the southern counties, including the secret weapons establishment at Porton Down, lead Triger and his assistant, Sarah Ambrose, on a perilous journey across the winter wilderness of the Welsh mountains to track the Killer and the unknown forces behind the threat.
Deep within the Snowdonia Range, Triger and Ambrose are stunned at what they eventually encounter, exceeding everything they could ever imagine. Will they escape the extreme danger in which they find themselves in and will they be able to stop evil forces from changing the British way of life forever?