TWO rather different leadership contests are happening this week. In the UK tomorrow, a new prime minister will be chosen, and in SA on Sunday, the Democratic Alliance (DA) will choose a new leader. The consequences of these choices will have hugely different effects.

The UK might count for less in the world these days than it did in its glory years half a century or more ago but it still matters a lot on the tables that count.

Today it musters, even after swingeing cuts in defence spending, the fifth-ranking military presence on the globe — the largest in Europe.

It is also, despite or perhaps because of its austerity programme, the fifth-largest economy on the planet. Its government boasted in January that the rise in employment was almost twice as fast as any other country in Europe.

The most successful British Labour Party leader, in terms of winning consecutive elections since the movement was founded in 1900, was Tony Blair. He once said: “The difference between being leader of the opposition and being prime minister is this: when I was leader of the opposition I used to wake up in the morning and say, ‘What can I say?’ Now that I am prime minister I ask, ‘What can I do?’”

Given the huge consequences of what Blair “did” in Iraq and Afghanistan, some — not least the restless tribes in his own left-leaning party — probably wished he had remained leader of the opposition.

But here at home — in a country way below the UK in terms of wealth and military clout and with sky-high unemployment — the official opposition DA will this weekend choose someone to say things on its behalf. He will need more than just one more heave or one more election to move from opposition leader to head of government, if he ever does.

SA’s place in the world, in the wake of lacklustre leadership, recent xenophobia, stuttering economic growth, electricity blackouts, investor switch-off and our ousting as the continent’s top economy, is less significant than it was in 1994, the year Blair was first elected Labour leader.

The outcome of the UK’s election on Thursday will be much closer fought and the composition of the new government more difficult to determine than any such contest in the country’s recent history, unless the converging opinion polls are wildly wrong.

In contrast, the DA’s congress in Port Elizabeth two days later will be more a quasi-coronation of front-runner Mmusi Maimane than a real humdinger, despite the equal merits of his challenger, Wilmot James. Political parties are moved by tides, and the current appears with Maimane.

Of course, the question of whether any party leader in a party-based, as opposed to a directly elected presidential system, hugely determines electoral outcomes is not as self-evident as it is widely assumed.

One recent opinion poll in the UK, amid a welter of daily soundings, stood out last week — the identity of the party leader would determine the choice for only one out of 10 likely voters.

In SA, something similar occurs. The outcome of last year’s general election had little to do with the perceived merits, or otherwise, of the ruling party’s president, Jacob Zuma, and his chief challenger, departing DA leader Helen Zille.

Zuma’s approval ratings before the election were in the low 40% range. Yet his party romped to victory with more than 62% of the vote, nearly three times the total garnered by the DA.

In the UK, of course, no one directly chooses the prime minister. This is a consolation of sorts to the geekish, though improving, Labour leader Ed Miliband, who still trails way behind Tory Prime Minister David Cameron in both the economic competence and the popularity stakes.

In the UK, while party identity is very significant, in marginal constituencies the popularity of an incumbent member of parliament can be just as determinative of outcome. In part, the British election consists of 650 separate contests in different seats. Despite the seeming grandeur of the electoral battle and breathless orations from party leaders about how “the future is at stake”, relatively few voters in a couple of dozen hinge seats will determine who enters the door of 10 Downing Street.

It is the voters and the candidates in such relatively obscure places as Warwickshire North, Bolton South and Solihull — to mention three of the top 10 most marginal seats — who hold “with their stubby pencils marking their ballots”, in Cameron’s words, the identity of the next prime minister.

But one thing the British election and the local election of the DA leader have in common is that both contests this week occur at a time, in very different places, of intense political fracture.

Forty years ago, nearly 90% of British voters chose between one of two parties: Labour or Conservative.

On Thursday, neither of those parties will have much more than 35% of the vote, if that. The rise of multiparty politics, and probably another coalition government, is due to the fracturing of the one-time duopoly in politics there.

The rise of the UK Independence Party in England and more significantly (especially for Labour) of the Scottish National Party north of the border has many causes. But nationalism and populism are two of the key ingredients for both of their surges, fuelled by the economic uncertainty of the world since the global financial crisis.

In SA, the fracturing is evidenced in other ways but also serves notice that while the ecology of our politics appears unchanging, both on the surface and beneath it, a tectonic shift in the electoral plates is taking place.

The African National Congress (ANC) has often invoked comparisons to Jesus to proclaim its longevity in office.

But while it has been a “house of many mansions”, as the Bible describes the “Kingdom of Heaven”, many have already left the building. These range from left-breaking populists, such as the Economic Freedom Fighters, to the disgruntled unionists who have left the Congress of South African Trade Unions.

Disaffection, not unity of purpose, is now a running theme in ANC circles.

This might not affect the next general election. But, like in a marginal British constituency, the next election here, for local government next year, is a much more parochial affair, but with equally large national implications.

Also, like today’s election in the UK, the outcome of the vote in the cities of Port Elizabeth, Pretoria and possibly even Johannesburg could be too close to call in advance and could also hinge on local personalities and factors.

This fracturing and uncertainty suggest that if he plays his cards right and if circumstances move in his direction, the next leader of the opposition in SA might have more to do than just think about what to say.