I feel that I foresaw in my previous answer that something like this might happen. And as I said in my previous answer, the employer can modify the contract given one week's notice. Furthermore, since he hasn't been there for 12 months there is no opportunity to take the employer to an Employment Tribunal - the employer will realise this, because sometimes the sheer hassle of doing it and the potentially negative publicity puts an employer off.
I don't think he can win this, and I think that the employer is being very unreasonable.