Hello, my name is XXXXX XXXXX it is my pleasure to assist you with your question today. Does the termination clause state that the notice period must be during term time, or is it just 6 calendar weeks?
Whether you resign or allowed to have your contract terminated would not really matter because in both cases you would be entitled to receive the same notice period from the employer. So if you wanted to ensure that this is dealt with as soon as possible and you are allowed to leave as quickly as you can, you may resign immediately and start the 6 week notice period. Even if you handed in your notice today, the notice would run until 29 April at the earliest so you may be expected to return for several days n the new term, unless you both agree that this will not happen. If he was intent on paying you then there is nothing you can do at this stage to minimise that as he may have already made up his mind. If that is the case you can certainly consider taking the matter further to the small claims court where such disputes are commonly heard.
he may mean it that you will be issued with notice f termination and that would be the end of the matter, but if he is trying to terminate it immediately then that would be a breach of contract on his part
it would be useful to have a formal rejection in writing for example to stop the employer from claiming you had either accepted the changes or that you implied doing so by not responding