This looks like a case for the UN! Certainly, the way ahead is likely to be through mediation rather than further confrontation and you do hold some cards in your hand to help you to bring this about.
The teacher is, in some respects, the easier to deal with. However well-based his or her comments may have been, it was not his place to make them and to have done so betrays a lack of professional judgment which might warrant an oral warning. Naturally, you have no wish to take such a measure in this case, but it may well be helpful if a member of your senior management team takes the teacher on one side to point out that continued intransigence might leave you with no alternative but to require an apology to be given.
At the same time - and delivering the other side of the bargain - you might wish the education welfare officer to call on the parent to discuss the issue, pointing out that the level of the provocation was not such as to justify such an outburst. He should be told that you would be well within your rights to debar him from entering the school premises, without appointment, a step you would be reluctant to take for the sake of the pupil, whose well-being is the concern of both parties.
You will note particularly that I have suggested the use of "go betweens" to do the negotiation. Your own position is such that, if you tried to do it yourself, however gently, it would be seen as threatening. In any case, you have to keep clear of the talking, in case you are obliged to take the very actions you are hoping to avoid.
Whether these strategies will work depends, of course, on the temperaments of the contending parties and the diplomatic skills of well-chosen mediators.
Following the reorganisation of local government, what happens to teachers who are offered new contracts on terms less favourable than those they previously enjoyed?
Under the Transfer of Undertakings (Protection of Employment) Regulations 1981, a transfer from one employer to another cannot be used to terminate an employee's contract. In other words, less favourable terms, which imply a termination of the existing contract and the initiation of a new one, are contrary to law and, if an employer persists, recourse may be made to an industrial tribunal.
A recent judgment of an employment appeal tribunal (Wilson and others v St Helens Borough Council) strengthened the position still further by asserting that the law applied even where the employees concerned had actually accepted new terms from the new employer. In other words, the teachers concerned were protected by the law, even from themselves.
Questions should be sent to Helpline, The TES, Admiral House, 66-68 East Smithfield, London E1 9XY. Fax: 0171-782 3200.