Here’s Labour’s record for the five decades years since the end of 1959: in government 19 years, out of government 31 years. Its best five decades were 1929-79, when it had 20 years in government, its worst just 12 in 1949-99. Of the 60 years since 1949 it has held office for 21 — one in three.
Reading that you’d think Labour had hardly been in power at all, but that’s more a result of the arbitrary 50 year time frame James has used. In terms of time in power, Labour did very well at the beginning of the modern party system and in recent years, with a bad patch in the middle (2nd and 3rd Labour governments).
If we look the history since Labour and National have been the major parties (I’ll be generous and include the ‘National Coalition’ Government formed after the 1932 election), Labour has won 11 of 25 elections and governed for 35 out of 77 years. Pretty close to even.
On the other hand, James gets it right when he points of that Labour has been more popular than National on average. He writes:
Yet in elections from 1959 to 2009 Labour’s vote-share average was microscopically more than National’s. Even if you put into the calculation the electorate vote share of 31 per cent in National’s 2002 disaster instead of the party vote share of 21 per cent, National led by only half a per cent.
In fact, you look at the entire history of the two parties’ contest from the 1935, rather than starting at 1959 for no particular reason, Labour has averaged 42.8% of the vote to National’s 41.6%. Despite winning more votes on average and most of the remainder going to parties to its left, Labour didn’t win office as often as National because of the undemocratic First Past the Post system.