Has a former UK party leader ever been expelled from their own party?

UKIP seems to have had a troubled relationship with a couple of its party leaders. Richard Braine, who led the party from August 2019, was suspended from the party while still in office over allegations of stealing data from the party. He officially resigned from UKIP a week later.

Additionally, while not a suspension/expulsion as such, Gerrard Batten, who led the party from April 2018 to June 2019, was blocked from standing for the leadership again in a motion entitled 'Gerard Batten has brought the party into disrepute by his actions and associations and should therefore not be allowed to stand for the leadership of the party' by the party's national executive committee.

Braine's successor, Freddy Vachha, who led UKIP from June 22nd 2020, was suspended from the party less than three months later, on September 12th, being replaced by former Tory MP and current UKIP Senedd Member Neil Hamilton. Vachha appears to be contesting the suspension. According to the party's statement:

Freddy Vachha has been suspended from membership of UKIP, pending a formal investigation of a complaint of bullying, harassment, verbal abuse and other conduct likely to bring the party into disrepute. Suspension from party membership automatically suspends Mr Vachha from the UKIP leadership.

It would be unfair to Mr Vachha give further details of the allegations against him prior to the conclusion of the judicial process. This will be conducted formally, impartially and subject to the rules of natural justice.

On a more historical note, it turns out that this has actually happened before in the Labour Party itself. Ramsay MacDonald, Labour's first Prime Minister, was expelled from the party after forming the National Government of 1931 as a coalition of Labour, Conservative, and Liberal MPs.

Most of the Labour Party was horrified and, for putting the national interest before party interest, MacDonald was denounced as a traitor to his class and expelled.

David Steel (The Lord Steel of Aikwood) was leader of the Liberal party from 1976 to 1988 when it merged with the Social Democrat party to form the Liberal Democrats. He then remained as joint leader of the party (along with Robert Maclennan) for four months.

Following his retirement from the House of Commons at the 1997 general election, he was given a life peerage and a seat in the House of Lords, where he remained a member of the Liberal Democrat party.

In May 2019, in the wake of revelations that he knew his former colleague Cyril Smith was involved in child abuse, Steel had the whip withdrawn by the Liberal Democrats during an investigation into his involvement. On 14th May 2019 the party concluded that there was no case to answer and Steel had the whip restored.

He has since retired from the House of Lords and resigned from the Liberal Democrats.