That's correct Colr6, it's a 1953 Nimbus. Wondered if they were known outside Denmark.
It was a Danish motorbike, produced at a factory called Nilfisk, best known for their fabulous alloy vacuum cleaners. They were very popular and used in large numbers by Mail Service, Police and Military. Has a flat iron frame, no rear suspension and a prop drive. Their straight cut gearbox makes a whinning noise which nicknamed them "the bumblebee"
I've done some repairing to this one, as well as giving it a fresh MOT. It arrived on a flatbed truck, because it only ran for 3 minutes at the time. Ii'll spent winter at my place, since the owner is rebuilding her house and the Nimbus was destined to live outside.