Started a "first clean" on a new res. custy in Bristol at 8.30 am. Finished at 9.30. Very cold, ice on the grass but water not freezing on ground.
Drove out to South Glos and started at 10 am and in the shade the drives were frozen. In a big city you do get two or three degrees extra of warmth compared with the countryside.
Finished last house at 3.30 - could have done another but would have had to drive for twenty mins and so didn't bother.