Original: The replacement program proceeded swiftly until 1940 , when the last pre-war conversion occurred , leaving only the South London trams and the subway routes 31 , 33 and 35 , the only tram routes operating into North London to survive the war .
Simplified: In 1940 , the last tram conversion took place before the Second World War . This left only the South London trams and subway routes 31 , 33 and 35 running .