I don't suppose it's exactly controversial to suggest that I and my party have changed over that period. Today I will argue that we've changed for the better.
Because my purpose here today is to explain, clearly and simply, what the Liberal Democrats offer the people of Britain, and why it's an offer which speaks to modern Britain.
Our offer is different from that of the Conservatives.
It's also different from Labour's offer. That won't surprise you.
What will surprise you, perhaps, is that it's different too from the offer of the Liberal Democrats in opposition.
What I want to set out is a case for why Britain should be governed from the centre ground. A case for both a stronger economy and a fairer society, because we can have both - they are not mutually exclusive.
Serious parties know that that the centre ground is the only place from which Britain can be governed. And serious leaders try to keep their parties in the centre ground.
But in times of economic distress, when people and parties are under pressure, when there are no easy answers, no silver bullets, only tough choices - at times like these, politics quickly becomes polarised as the homing instincts of ideologues to the right and the left kick in.
The Tory right dreams of a fantasy world...
where we can walk away from the EU, but magically keep our economy strong...
where we can pretend the world hasn't moved on, and stand opposed to equal marriage...
where we can refuse to accept the verdict of the British people and pretend the Conservatives won a majority of their own.
The Labour left lives in a different, but no less destructive, fantasy world...
where their irresponsible borrowing in government can be remedied by borrowing more...
where every budget reduction can be opposed without explaining where the money should come from...
where games can be played with political reform and EU budget policy without long-term damage to their credibility.
It is at times like these that Britain needs a party rooted in the centre ground, which anchors the country there.
The Liberal Democrats are that party. We're not centre ground tourists. The centre ground is our home.
While the tribalists in other parties desert the centre ground under pressure, the Liberal Democrats have done the reverse. Under pressure, we've moved towards the centre.
Governing from the centre ground means applying pragmatic liberalism to the policy challenges of our time.
But pragmatic liberalism is not the same as dogmatic liberalism. And that is what distinguishes Liberal Democrats in opposition from Liberal Democrats in government.
The greatest strength of our party is our idealism. But in our strength lies our weakness - because sometimes idealism can turn into dogma, or at least an unwillingness to engage fully with the day-to-day experiences and perspectives of the British people we seek to serve.
A party of government knows that workable solutions need to be grounded in values - but also that they must respond to the hopes and fears of reasonable people.
This is the lesson we've learnt in government. The challenges of governing at a difficult time have given us a harder edge and a more practical outlook.
It's worth pausing here for a moment and making a point about the immediate future of my party. There are two alternatives.
If we are to become a more permanent fixture of government, then it will be, at least at first, as a partner in coalitions.
That means embracing the realities of coalition government, and becoming better and better at negotiating successfully on behalf of those in Britain who expect us to stand up for them.
It means accepting compromise.
It means putting up with people who object that we haven't got everything they wanted, and who can't see the value in getting much, much more than we ever could in opposition.
Because that is the alternative - a retreat to the comfort and relative irrelevance of opposition.
But - and let me make this very clear - choosing opposition over government is not a values-free choice.
It is a dereliction of duty. Because if our values and principles matter to us, we should want to see them deployed for the good of the British people. It's not about us, after all. It's about the people we serve.
Let me offer an example of how, in government, the Liberal Democrats have tacked towards the centre, not away from it.
In opposition, it would have been easy to decry the less pleasant consequences of austerity. No matter how rational opposition parties try to be, it's just too easy, too tempting, to go for the quick win. That's why opposition parties are so good at spending 'savings' two, three or four times over. Play budgeting with play money.
But in government, we've not been able to do that.
We know from experience now: if you protect the health and education budgets, as we correctly did, you can't oppose every reduction in the welfare budget.
If you want to protect welfare as well, you've got to accept that you'll end up gutting the crime budget, or the BIS budget, or local government. We get that now. We've learnt to live with a host of invidious choices.
Another example: in these distressed economic times, the ideologues to left and right find comfort in the shibboleths of their preferred economic doctrines and turn their backs on evidence and reason.
So the prescription of the right is all supply-side - deregulate, cut, get out of the way.
The prescription of the left is all demand-driven - tax, borrow, spend, intervene.
In government, we've rejected these Manichean alternatives and stuck with a more flexible approach.
Yes, we have to cut expenditure to bring down the deficit. Otherwise we put ourselves in hock to the bond markets, drive up interest rates and impoverish future generations.
And yes, we have deregulated:
We've stripped back accountancy rules for the smallest businesses.
We've simplified the rules around maternity leave and flexible working.
We've extended the qualifying period for unfair dismissal so businesses can be confident about hiring new staff.
But we have also taken steps to drive demand:
We've put money back in the pockets of the low and middle income families we know are most likely to spend it with our income tax cut.
We've taken every opportunity to increase investment in capital - infrastructure, roads, rail, schools
We've established the Regional Growth Fund, the Growing Places Fund and multi-billion pound Treasury guarantees for investment to unlock private sector growth.
We have resisted the false choice between a state that steps in and assumes control, and a state that backs off and washes its hands.
We have embraced the challenge of building an enabling state that acts where necessary and backs off where not…
Promoting, inspiring and facilitating growth and opportunity.
But recognising that the strong economy we want can only be built on the back of hard work and responsibility by citizens themselves.
So we've been on a journey. But our journey has been towards the centre ground, not away from it. Because the centre ground is where liberals are best able to fulfil our purpose in politics.
For Liberal Democrats, our purpose is to enable every person to be who they want to be and to get on in life. Freedom and opportunity combined. Or what the philosophers might call 'substantive freedom'.
To deliver on our purpose, we need to build a stronger economy in a fairer society.
We need a stronger economy because without resilience and sustainable growth, our economy will never be able to deliver the jobs and the opportunity people need.
We need a fairer society because unless we ensure everyone has the means to get on, some will be left behind while others race ahead, and our society will become increasingly unfair and unequal.
And so every policy we promote has to make our economy stronger and our society fairer.
What underpins our 'stronger economy, fairer society' agenda, and gives it a distinctly liberal flavour, is a very clear conception of the appropriate balance between the role of the state and the role of the citizen.
For us, that relationship is clear: it is the government's responsibility to ensure every person has the opportunity to get on, but every person must take personal responsibility for using those opportunities by working hard.
We cannot absolve people of their responsibility for improving their own lives, because to do so would be to turn them into dependants - and so deny their agency and compromise their dignity. You can't build a stronger economy with people lost to dependency.
At the same time, we cannot wash our hands of those without the means and advantages to get on in life alone. To do so would compromise their potential and diminish their dignity - a tragedy for them and a waste for society. You can't build a fair society when you deny some the chance to fulfil their potential.
Our commitment to opportunity has deep roots. Liberals have an unshakeable belief in human potential. We know that children born in the most difficult circumstances can rise above them and live the fullest of lives - but only if they're given the help to do so.
Parents know what I mean. You look at your children and yearn with hope for their future. You do whatever you can to give them every advantage. You worry about the obstacles they will face, and you plan to help them overcome them all.
But equally, parents know that kids need to learn to look after themselves. Slowly but surely, we guide them into independence and adulthood. Because we know that to be happy, they will need the means and capacity to run their own lives - and pass their love and skills on to the grandchildren they might give you one day.
Parents know instinctively that a balance of opportunity and responsibility are what human beings need to thrive. Why would the state treat people otherwise?
And so we need both - a stronger economy and a fairer society; more opportunity and more responsibility.
Every one of our policies needs to meet this test.