It may seem a little early to contemplate David Cameron's memoirs but I can imagine already what form the opening chapters will take. When he looks back at his years in opposition he will explain with justified satisfaction how he got his party off its knees and mounted a recovery. He will also express two big regrets.

The first regret will take him back to his leadership campaign in 2005 when he pledged to take his party out of the main centre-right grouping in Brussels. The second will bring him closer to the current pre-election frenzy and his decision to make so much of Britain's "debt crisis". I do not believe that these will be fleeting asides in Cameron's memoirs, but overwhelming themes. In a way that is easily underestimated, what is said and done in opposition shapes the future contours of power and act as a severe constraint. Read the retrospective thoughts of Wilson, Heath, Thatcher and, shortly, Blair. They came to realise for good or bad that their words and deeds out of power determined what followed once they had won.

On Europe Cameron will come to recognise that he was trapped from the beginning. His promise during the leadership campaign to pluck the Tories away from the centre-right European People's Party (EPP) in Europe might have seemed logical at the time. In opposition the easiest routes have a deceptive allure. Cameron needed votes of several Eurosceptic MPs in the contest, or thought he did. To his credit David Davis, Cameron's opponent, argued that withdrawing from the EPP was a step too far. Cameron saw a gap and went for it.

Download the new Independent Premium app Sharing the full story, not just the headlines

After Cameron had secured the leadership and was making "Blair-like" initiatives, he claimed there was no equivalent to Labour's "Clause Four", a symbol of his party's marginalisation that he could slay dramatically. He was wrong. Europe is the equivalent for the Conservatives. The party is still obsessed, even if it will not play to the gallery during the conference this week. Cameron should have taken them on over the issue at the beginning of his leadership, but of course he could not do so. He would have lost the battle and anyway he is, at this point, on the Eurosceptics' side.

Already Cameron's failure to challenge his party leads to a perverse contortion, a promise to hold a referendum on the Lisbon treaty and then public evasiveness over what would follow ratification. For a leader who has made honesty versus dishonesty a convenient dividing line he is being dishonest because he dare not be candid with his party, or rather his party is too strong to be challenged.

He will come to deeply regret his weakness over this issue when in opposition. He is intelligent and flexible enough to recognise, at some point, that it is in Britain's interests to be a player in Europe when the patterns of the world are determined by a plethora of unsteady superpowers. Seeking to be a "Blair-like" player on the international stage, he will be uneasy when Merkel and Sarkozy unite in defiance of his own outdated views. Yet he will be able to do little about it.

Of course he would not hold the referendum after ratification, but he would seek to renegotiate some more opt-outs from the Lisbon Treaty, even though Britain already possesses more opt-outs than it needs. I predict there will be calls for Britain to opt in to some "opt-outs" before very long, especially those relating to crime. Still, if he wins, many of Cameron's MPs will watch those destructive negotiations like hawks and will not be satisfied with a token gesture. They will have every right to be hawk-like as Cameron has not discouraged their fervour, and it will be too late to change a party if power is secured. Opposition is the only time where there is space to instigate internal reform.

Cameron's later decision to play up the "debt crisis" will take up even more reflective melancholy space in his memoirs. There is a tendency for British governments to panic in economic crises and make matters worse. Denis Healey's memoirs provide a prophetic insight into what Cameron will write in a few years' time. He admits that, as Chancellor, the Treasury overestimated the need for spending cuts in the mid-1970s. Its figures were wrong. Healey admitted that those in the cabinet who were arguing that the axe had fallen too savagely proved to be right. Now we do not have to look back or ahead. Most distinguished economists regard the Conservatives' obsession with the level of debt as over the top. Samuel Brittan was the latest (in the Financial Times last week) to warn that Cameron is making too much of it.

As with Europe, the chosen path must have seemed so tempting. How does an opposition in Britain claim that this country's recession is uniquely the consequence of its Labour government? Cameron chose to do so by claiming that Brown's "debt crisis" was incomparably worse than elsewhere. The shift has worked for him beautifully in opposition, realigning his leadership with right-wing activists and newspapers. But over time, Cameron will come to realise that his stance obliged him to cut more deeply and quickly than necessary, jeopardising reforms that cost money in the short term.

Opposition is exceptionally challenging, closer to an art than a science. But whatever the chosen route towards power, the words that accompany it matter hugely. In the spring of 1997 Tony Blair confided to Clare Short: "Don't worry. We will be more radical in government." Predictably New Labour was less radical, constrained by cautiously evasive commitments made in opposition. After resigning, Blair expressed regret that he did not do more in relation to public services during the first term. He will write about it in his memoirs. He could have done more, but chose not to make the arguments in opposition.

Alastair Campbell revealed recently that Blair's biggest regret was that he did not get Britain into the Euro. But Blair was never going to get the chance to do so after he decided in opposition to offer a referendum on the issue and to declare at the same time that he "loved the pound". Blair's regrets are rooted in what he said and did in opposition. Similarly Cameron has hinted at being more radical in power. He will be less so. Power is more complicated and daunting than opposition. What is more, there is always another election to win.

By most measurements Cameron has been a successful leader. He has been reliably calm under fire, an engaging communicator and a leader who has given space for some of his allies to develop innovative ideas. But in retrospect he will also have a tinge of regret about this pre-election gathering. So far he has pulled off the trick of personifying change, but with talk of Europe and benefit cuts dominating Manchester, it feels closer to a Tory conference from the early 1990s, although one that is more sensitively choreographed and tonally perfect – serious but not triumphalist.

Speaking to some of the younger candidates and policy advisers, I sense a gush of youthful energy, but then the old issues surface to remind us their party is not as fresh as it seems. As I write, Sky News is showing the famous clip of Peter Lilley as Social Security Secretary attacking in verse those on benefits.

I wonder how long it will be before Cameron writes his memoirs.

s.richards@independent.co.uk