As an employment attorney, I see nothing wrong with the response - it appears to say that men and women should be treated equally and judged on the merits. I do not practice in England, however. Also, you say that you don't know his response verbatim.
If this was truly his response and if they told him that it was because of that response that they are asking him not to stay on, then I could see how this could be turned against them as discriminating against male, which I think England prohibits. This might however be difficult to prove. I also find it difficult to understand that they would use a question that he answered in confidence as a basis for firing (which they did if they asked him to leave)
I could also see how one could make the argument that the answer was confidential and gender neutral, and therefore the real reason for the request that he leave must be something else.
Having said all that, I am not an expert on English employment law (and also, you say he is not an employee...). I would fight this (if doing so doesn't mean that marks him somehow in the eyes of other employers because this gets around).







