From the THE SCHOOL TEACHERS’ PAY AND
CONDITIONS DOCUMENT (STPCD) on the NUT website:

27. The STPCD requires that a teacher undertakes to work, “such
reasonable additional hours as may be necessary to enable the
effective discharge of the teacher’s professional duties.” This
includes, in particular, planning and preparing courses and
lessons and assessing, monitoring, recording and reporting on
the progress of assigned pupils. Although this may be time
spent doing work under the general direction of the head
teacher, unless it is part of PPA time, it is not “directed time”
within the 1265 hours. See also paragraph 40 on PPA time.

While it is said to be up to teachers how much time will be spent on these addtional duties, just think about writing reports for a class of thirty primary school children on all subjects as one small part of the planning, assessing etc. The 1/2 day PPA time (2.5 hours) is a help but there is much more involved than that.

I am actually now a University lecturer and my 'directed activity' is 1500 hours per year and that, again, does not include anything like the real time it takes to prepare, carry out and assess my work. And we have a leave allowance of 35 days p.a. not the months off people always assume.