I managed to get the car to struggle along in first and into a car park where the brakes eased off.But i then found the brake pedal ,although solid had no braking effect at all and had to use the hand brake to limp home.The temp was below zero.

When I started the car to visit local shops the coolant light stayed on but as I had only recently checked the level and the temp was below zero and the journey short I proceeded with my journey.I later checked the level was correct. Any ideas?

The brake servo not working , if leaking fluid your pedal would go down to the floor , seems to me no brake servo or vacuum to operate it.

I strongly suspect a brake servo or master cylinder problem.