The historic British Liberal Party imploded probably around WWI. I think the rot was set in when Asquith was the Prime Minister - the Liberals were entering a phase of becoming more socialism-ized which were identical to the routes the then-new Labour Party was following. Another bad news was their free-trade wing was being eaten alive by the Conservatives, which added this faction to the old-fashioned old rural, hierarchical wing.
In fact, had the Labour Party not entered into the fray, it seems the British Liberal Party would still move further to the left and occupy where Labour is in our world's Britain (or like a carbon copy of its namesake in Canada).
Curiously, the historical 19th century British Liberal Party encompasses what the United States's mainstream political landscape looks like. Its conservative wing is where the US Republican Party today is, while its left-wing will be where the US Democratic Party of today lies. In those days the British Labour Party would be to the US Democrats' left, while Conservatives (the High Tory faction) would be to the right of US Republicans.