'Meanwhile, the Liberal Party declined rapidly, and the party also suffered a catastrophic split which allowed the Labour Party to gain much of the Liberals' support. With the Liberals thus in disarray, Labour won 142 seats in 1922, making it the second-largest political group in the House of Commons and the official opposition to the Conservative government. After the election Ramsay MacDonald was voted the first official leader of the Labour Party.' - https://en.wikipedia.org/wiki/Labour_Party_(UK)#Early_years_(1906%E2%80%931923)
General strike capitulations didn't come until 1926 afaik.