It provided a mechanism for a Member of Parliament who was judged to be of unsound mind to be removed from his seat.

The most celebrated of these was John Bell the MP for Thirsk who in July 1849 was found to be insane by a commission of enquiry.

[3] His determination was such that despite being a private members bill it went through all its parliamentary stages with little opposition,[4] in less than five months and received its royal assent on 10 May 1886, hence becoming the Lunacy (Vacating of Seats) Act 1886.

In practice there was a reluctance to call on the Act and it was only used once in the rather special circumstances of the First World War.

In August 1916, in these circumstances, Charles Leach the MP for Colne Valley was declared of unsound mind and relieved of his seat.