LONDON - The simplest explanation for British Prime Minister Theresa May's decision to hold early general elections a full three years before they are due is that early ballots clearly favour her government; all opinion polls indicate that her ruling Conservatives enjoy a double-digit electoral lead over the main Labour opposition.

However, Mrs May is aiming higher: she wants to get from the elections, now scheduled for June 8, a decisive mandate to negotiate Britain's exit from the European Union. And she also hopes to marginalise separatists in Scotland, who are demanding another referendum about the territory's independence.

Yet the electoral campaign which now lies ahead will be gruelling, intemperate and full of risks even for a prime minister who otherwise enjoys healthy popularity ratings.

Since she came to power last June in the wake of Prime Minister David Cameron's failure to win the referendum over Britain's continued membership in the EU, Mrs May has had to tolerate jibes that she is has no mandate to govern.

In purely constitutional terms, the criticism is irrelevant; elections in Britain and in all countries with a British-style system of government such as Singapore are about parties rather than individuals, and whoever is the leader of the biggest party is also prime minister. Still, the fact that the Conservatives gained a slim parliamentary majority over all other parties at the 2015 general elections hampered Mrs May's room for manoeuvre.

And her slim majority was even more difficult to sustain given the serious decisions the British Prime Minister was called upon to make in Europe. Mrs May opted to pull Britain out of the EU's single economic market, and promised to reintroduce border controls on EU citizens, a position which came to be known as "Hard Brexit", but a stance which was resented by at least 80 of her 331 MPs, who want Britain to remain closely connected to the EU.

By opting for early elections, Theresa May is not only silencing opponents within her own party, but also rebuffs anyone hoping that she may change her mind; "Britain is leaving the European Union and there can be no turning back" she curtly explained yesterday.

And by waving the national flag with promises that, under her government, Britain will "chart its own way in the world" and regain control over its borders, laws and money, Mrs May is also cornering her Labour opponents, who will find it difficult to articulate their own European stance.

Most of Labour's existing MPs support Britain's continued membership in the EU, but the majority of Labour's electorate, particularly in the northern parts of England, voted to leave the EU. Jeremy Corbyn, the party's unpopular far-left leader, will struggle to paper over such divisions, especially since he is an awful campaigner; current projections are that Labour could be heading for its worst electoral defeat in generations.

And better still from the government's perspective is the possibility that the Scottish National Party, which controls 56 seats in the outgoing parliament, may lose a few seats, thereby boosting Prime Minister May's position, which is to refuse holding another referendum on Scotland's potential separation from the United Kingdom.

But although the prime minister appears to have chosen her electoral targets with great care, she is also taking some big and risky gambles. The first risk is that her own party could come across during the electoral campaign as divided as Labour is on Europe, thereby ruining Mrs May's carefully-calculated image of steely determination.

There is also the risk that the Liberal Democrats, traditionally Britain third-largest party, could eat into the Conservatives' vote; the Liberals remain enthusiastically pro-European, and could attract younger British voters who are frustrated by the anti-EU sentiment which now dominates the country's political elite. So, while Mrs May is certain to win seats from Labour, she could also lose a few to the Liberals.

And although the Scottish Nationalists can hardly do better than the huge victory they scored at the last general elections when they went from 6 to 56 electoral seats, if they manage to hold on to most of their seats that would be interpreted as a rebuff to the British government and may well precipitate fresh demands for Scottish independence, precisely what Theresa May is keen to avoid.

Still, the temptation to gain a fresh mandate for the next five years proved too difficult to resist. And the Prime Minister's timing is clearly shrewd; as Mrs May openly admitted, she has "a one-off chance" to get the ballot out of the way "while the European Union agrees its negotiating position, and before the detailed talks begin".