"What we are doing is putting contingency plans in place, and what we will do is have 3,500 service personnel held at readiness -- including regulars and reserves," he said.

Williamson said the soldiers would be ready "to support any government department on any contingencies they may need".

Britain's cabinet on Tuesday agreed to make no-deal Brexit planning "an operational priority", as Prime Minister Theresa May struggles to persuade MPs to support her Brexit deal.

British police chiefs have also drawn up plans for possible "civil disorder leading to widespread unrest", according to a leaked plan published by the Sunday Times in September.

The document was reportedly prepared by the National Police Co-ordination Centre, which is responsible for coordinating police deployments during large-scale events and at times of national crisis.