The Communist Party of Great Britain was refused affiliation to the Labour Party between 1921 and 1923. 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 the now-rehabilitated Ramsay MacDonald was voted the first official leader of the Labour Party.
What was the third largest group in the House of Commons?