It is more than 14 years since I stood chatting to a nervous politician on the eve of taking power.

The Tories' coalition talks with the Liberal Democrats had concluded and, the next day, David Cameron – for whom I had been working as a speechwriter – became the youngest prime minister for almost two centuries.

Having ousted a tired and fractious Labour Party, Cameron promised to deliver 'a new politics where the national interest is more important than the party interest'. How hollow those words sound today after the traumas of Brexit and four more Tory prime ministers.

Yesterday, I cast my vote for Labour in what seems certain to be the most transformative election since Cameron's triumph.

Like millions of my fellow citizens, I backed Sir Keir Starmer more in hope than in the expectation that he will solve our nation's glaring problems. My decision was fuelled by despair over the corrosive failures and constant in-fighting destroying the Tories.

Their pathetic campaign underlined how they are lost, lacklustre and out of touch – while the Royal Mail's inability to deliver postal votes symbolises the pervasive sense that nothing in the public space seems to work properly any longer.

Starmer's message of change struck a chord when trust in police has fallen to a historic low, prisons overflow, rivers are polluted with sewage and patients must wait painfully long to see their dentist or doctor.

Behind his bland exterior, the Labour leader has proved to be a smart, ruthless and pragmatic politician. He has, after all, managed to pull his divided party back from major defeat five years ago to what pollsters have predicted will be a massive majority.

Yet he remains mysterious to voters. I know him through our shared love of Sunday football in North London and I like him, even if I have a clearer understanding about his style of play as a dogged midfielder than where he really stands on the political spectrum.

Certainly he merits criticism for backing his predecessor Jeremy Corbyn. Yet such political suppleness – a polite word – has taken him to the doors of Downing Street.

And unlike Corbyn and his repellent band of hard-Left acolytes, this former Director of Public Prosecutions passes the most important test for a prime minister: He can be trusted with Britain's national security.

He is a serious and focused figure who proved his determination to detoxify Labour and drag it back to the centre by wrapping it in the flag despite internal resistance.

Now he will be challenged by the need for tough action, rather than simple stunts, in these tremulous times – and he has not shown the surest touch on the global stage in his response to Israel's attack on Gaza following the Hamas atrocities.

He must instantly take a leading role in the fight to defend democracy against an aggressive alliance of dictators – and his stance could be crucial if key allies such as France and the US shift to the populist right in their own elections. 

He would do well to bind Britain close to the likes of the Baltic States and Poland who clearly see the threats we face from Russia and China. But only time and his response to events will show if he has the requisite fortitude and vision.

The need to rearm rapidly like Poland – where there is political consensus to double defence spending – demonstrates the conflicting challenges Starmer faces on the domestic front that will define his premiership from day one.

He must fix many public services in dire need of both reform and money – but at the same time restore faith in our political system, which has collapsed due to a string of issues from the Iraq War debacle and Westminster expenses scandal through to Brexit, immigration and the handling of Covid.

So can he really find mountains of cash to sort public services while driving though tough reforms that might anger key groups and unions in his party? And do this without infuriating voters who gave him power based on such a shallow manifesto?

This is a Herculean challenge. Bear in mind the British Social Attitudes survey last month delivered a barrage of depressing data revealing how trust in Westminster and Whitehall has plunged to record depths.

Cameron pledged to tackle this crisis of confidence more than a decade ago. Now Starmer says the same – and this task has become even more crucial and difficult in this era of artificial intelligence, social media and misinformation peddled by our enemies.

Labour's suggestion that magical economic growth, better productivity and smarter use of technology will come to the state's salvation is the stuff of political fantasy.

Starmer ducked the question of ramping up spending to boost our shrunken Armed Forces – like he dodged many important questions in his cautious march to power – by saying he would match a Tory pledge to push it up 'as soon as resources allow'.

Defence is also a sector where shocking procurement scandals have wasted huge sums of taxpayers' cash, demonstrating the obvious need for fresh thinking along with genuine reform.

Health spending surged under the Tories, with the number of doctors and nurses rising fast in recent years – yet the NHS remains sick with swollen waiting lists and tormented by poor treatment outcomes compared to similar countries.

It is great that Labour's leadership has come to accept the arguments I have been making for almost two decades about the need to stop worshipping the NHS, which masks its many flaws and faults. But do they have the stomach to spark serious debate on its future?

The public is rightly frustrated over collapsing social care with endless talk of reform that gets fudged – but Labour has offered little more than the usual platitudes about a need for cross-party consensus, a fair pay agreement devoid of funding detail, and the concept of a 'National Care Service', lacking clarity on what this means.

Meanwhile Starmer knows that his party's recovery after such resounding defeat in 2019 demonstrates the volatility of a disgruntled electorate – and that Labour could quickly become as unpopular as the Tories.

The Liberal Democrats will offer little opposition since barely diverging from Labour, and the shrivelled Tories may carry on their destructive civil wars in opposition. But an emboldened Nigel Farage waits in the wings – possibly with a new platform in Parliament to seize on any mistakes, stoke fresh divisions and stroke his huge ego.

I worry that Starmer may be too cautious, too consensual and too lawyerly to dare tackle the profound problems that plague our country with the tenacity he displays on the football pitch. I am encouraged, however, by his contentious pledge to build on poorer quality Green Belt, a sacred cow that needs slaughtering amid the urgent need for more housing.

He might also be too influenced by Tony Blair, since the last but one Labour prime minister has used his massively resourced think tank – part-funded by tech billionaires and advising some of the world's worst regimes – to extend his tentacles back into the party.

But I supported Starmer since the Tories deserve to be ousted – and he is right that Britain desperately needs change.

Now I hope that if the weary electorate entrusts him with a giant majority, he will use the opportunity to display boldness, drop any Blairite trickery and be honest with the public over the scale of our domestic and global challenges.