No. The teachers must work under the reasonable direction of the head at such times and such places as he or she directs. This clearly includes working outside school premises, where appropriate, and many teachers do so. Probably one of the most common examples is taking pupils to a local swimming pool for lessons. Your situation is very similar. Unless the teacher can show that what she is required to do is unreasonable, she should accept it.
The school secretary has acted as clerk to the governors without extra pay for many years. She now says that the workload has increased, the hours are unsocial and she wishes to cease. Am I entitled to regard this as part of her contractual duties? Whose job is it to arrange for a replacement?
This task is only a part of the secretary's duties if it says so in her contract, or letter of appointment. You might argue that custom and practice has made it part of her contract, but this would be a singularly ungracious way of responding to what has been service well beyond the call of duty.
I have never much favoured secretaries doing this job, though I accept there is often no alternative. It may be argued that the secretary is too close to the head to offer the governors the dispassionate guidance they should get from a clerk.
It is governors' responsibility to appoint a clerk directly, if the school is a foundation or voluntary-aided school, or to select a clerk for the local education authority to appoint, if it is a community school. They have the power to pay clerks. Many LEAs offer a clerking service and provide training. The best solution might be to advertise.
We have created gaps in our school fence to allow neighbours to cut across the playing field. Previously the fence had been vandalised to gain access to this route. Are we liable for any accident that occurs to people using this short cut?
I should not think so, unless it could be shown that you had negligently or deliberately created the situation in which the accident occurred.
Nevertheless, I think you, or the LEA, should post a notice indicating no public right of way exists. Even that might not protect you against liability for negligence. Nevertheless, you have provided a common-sense answer to a problem and I do not believe that your liability is greater than it was when people broke the fence to get in.