This is the highest daily case number recorded by the UK according to CNN's tally.
This tops the previous record of 35,383 cases reported on Thursday.
A further 326 deaths were recorded in the UK on Sunday.
Medical Director for Public Health England Yvonne Doyle said in a statement on Twitter that the "sharp and sudden increase is of serious concern."
Doyle said most of the new cases "reported today are concentrated in London and the South East" although it is "too early to tell if this is linked to the new variant."
This number comes as nearly 20 million people in the UK are placed under the highest level of restrictions.