Dodros: A school may be within its rights to assert ownership of teachers'
lessons and students' work - using those, for example, to make money by selling teaching materials, without remunerating those who have created such resources.
Tafkam: From the Copyright, Designs and Patents Act 1988: "Where a literary, dramatic, musical or artistic work is made by an employee in the course of his employment, his employer is the first owner of any copyright in the work subject to any agreement to the contrary."
Teacher: Write your lesson plans out, store them in hard copy (post it to yourself dated recorded delivery for example) and then offer to use these ideas when working. The intellectual rights belong to YOU. However, you would need to come from the "I am using my own work in my teaching job"
angle. Anything you write "for your school" is much much more complicated.