I would appear that there are in fact rules about nutters and lunatics in Parliament.

The 1886 act was superseded by the Mental Health Act 1959, which in
turn was replaced by the act of 1983, section 141, which says that an
MP suffering from a mental illness and authorised to be detained can be
removed from parliament.

Seems something of a pity that it’s not actually enforced.

But incapacity alone is not a disqualification.

Ah, that’s why: they’d have to clear the whole place.