It varies slightly from council to council and between state schools and fee-paying schools, but they are generally close.
A cut and paste from the City of Westminster schools webpage:
SPRING TERM Monday 6 January - Friday 14 February 2020
School holiday Monday 17 February - Friday 21 February 2020
Monday 24 February - Friday 3 April 2020
School holiday Monday 6 April - Friday 17 April 2020
(Easter weekend 10 - 13 April 2020)
SUMMER TERM Monday 20 April - Friday 22 May 2020
(May Day Bank Holiday will be taken on 8 May 2020)
School holiday Monday 25 May - Friday 29 May 2020
(Spring Bank Holiday will be taken on 25 May 2020)