Sacking push 'mixes' two separate issues
If a teacher acts in a way that is incompatible with his or her duties, then he or she can be suspended and then dismissed. These cases are relatively straightforward. It is more difficult when they fall below acceptable standards (in employment law the correct term is lack of "capability").
The most difficult cases are those where performance is inconsistent, and the cause may be outside the school and therefore impossible for the headteacher to deal with. The minefield is the Employment Protection (Consolidation) Act 1978 which correctly places the responsibility for proving lack of capability on the employer. Most LEAs have well established procedures which can avoid the traps of wrongful, summary and unfair dismissal.
It is not easy for heads to manage the capability procedure when what the teacher really requires is sensitive support. But pupils should not get second best. If the capability procedure is applied as a strategy for improvement, rather than a preamble to punitive action, then heads may be more willing to use it as a normal management tool for improving standards.
Martin Baxter is an LEA inspector