I am getting old. Like most old men I have a tendency to be grumpy and claim that things aren’t as good as they were in the old days. Please bear this in mind when you read this.

I was trained as a Commando officer so I don’t know any other means of tackling a challenge than fix bayonets and charge. I don’t really do subtlety. Please remember that, too when you read on.

I am an enthusiast, and have a tendency to paint in large shapes and bright colours. What follows is Gaugin, not Canaletto. Please make allowance.

When you read this please finally note that I have been a committed and passionate Liberal since a canvasser knocked on my door forty-five year ago and explained what we stood for. That day, I put on Liberalism like an old coat waiting for me in the cupboard and I have worn it ever since with pride – come what may.

In all those long years I have never glanced to right, left or centre for a better political home for my beliefs than our Party – and that remains the case still. So please understand, if the words which follow offend, they are written with love.

So, now you have been warned, here goes.

There are good things – really good things – to celebrate as we gear up for Bournemouth. We have a multi talented Leader who deserves our whole-hearted support. We have 12 MPs in place of 9 before the last election. We still retain thousands of new members and we are winning local Council by-elections at a good rate.

But – didn’t you just know a ‘but’ was coming? – nevertheless, the biggest danger for our Party at the seaside next week lies in glossing over the existential challenges which now face us. Unless we are prepared to be realistic about where we are, return to being radical about what we propose, recreate ourselves as an insurgent force and re-kindle our lost habit of intellectual ferment, things could get even worse for us.

Consider this. We are the Party who, more than any other, represents the progressive centre in our country (I prefer centre left, but I am not in the business of dividing here). That space has never been more empty, voiceless, vacant and uncontested than it was in the last election. And yet far from filling that gap and mobilising those in it, our vote went down to an even lower base. Not in my life time have their been conditions more favourable for a Lib Dem advance in a General Election. But we went backwards.

Now, with Labour and the Tories spinning way to the extremes, Britain is polarised as never before and the vast sea of people who share our beliefs, find themselves voiceless and silent.

Not all of them, sadly, are Liberal Democrats or want to be. Many belong to other Parties and many, many more do not belong to any party – or wish to, with party politics as they are.

Politics in Britain is unsustainable in its present state. The moderate, majority voice of our country, which usually determines elections, cannot be left so unrepresented. If we cannot, or will not be the gathering point for these, the new left out millions, then who will and what are we for?

Twice before in our recent history, others have moved onto our ground– once with the SDP and once in the early days of New Labour. Both times we reached out to these new forces and prospered as result. These days we look hostile to this possibility. We will be at very grave danger indeed if this should happen again in the near future and we stand aloof.

Our reluctance on this front does not just threaten our future. It also contributes to the disfigurement of our national politics. If we are to fulfil our historic role at a moment when liberalism is more at threat than ever in my life, then we have to be less tribal, more inclusive and more willing to engage others than we have sometimes seemed in recent years.

What does this mean?

I do not oppose local electoral deals where they make sense. But I do not think they are the answer. These so-called “progressive Alliances” are almost always anti-Tory and always end up denying voter choice. Political partnerships work best when they are for something better, rather than against something worse.

Any attempt to create a new framework for our politics should begin with widening the space in which we can make common cause with people who share our values, rather than harping on about the things that separate us. We should not find it impossible to work with individuals in other parties and none (including, yes even Tories) who share some cardinal principles we jointly believe in – say, creating a green economy, tackling the gap between rich and poor, working to reform our political system, rejecting isolationism and sustaining a market system which serves the individual not the economically powerful.

If this strategy is to work for us, it must be confidently led from the top, not just mildly tolerated at the top.

Here’s a proposition.

Why could Lib Dems not lead in launching a series of studies which brings in those of other Parties and none to make proposals on some of the big issues of our time, as Norman Lamb has done so brilliantly on Health. Issues such as creating a green but successful market based economy; sorting out the fabulous mess of our broken constitution; spreading wealth in the age of robotics and artificial intelligence; adopting a foreign and defence policy more appropriate to our fractured, unravelling world– I am sure you can think of others. This worked well for us in the past; the Cook/Maclennan Commission paved the way to the great surge of devolution of the late 1990s; the Lib Dem sponsored Dahrendorf Commission on Wealth Creation and Social Cohesion in 1995 gave us great credibility and a host of new ideas.

The Chinese philosopher Sun Tze said “Strategy without tactics is the longest way to victory. But tactics without strategy is the noise before defeat”. Winning by-elections and distributing Focuses are a tactic, not a strategy. Our strategy should be to do whatever we can, whenever we can and wherever we can to work with all those individuals in other parties and none, who share our values and want to join us on the great enterprise of re-shaping and renewing our broken politics.

Consider next, this.

When I joined our Party we had been, for the best part of a hundred years, a radical and insurgent party and remained so right up to the moment when being insurgent became popular – when we became the Government. Now people see us, not as a force for change but as a part of the establishment. Whether we could have been insurgents in Government is a question for history. The question for now is; there is a hunger for change out there, why don’t we any longer look or sound like the people to bring it?

There may be many reasons for that. But the biggest one is that we are doing very little new thinking and producing very few new ideas.

The party I joined all those years ago our Party was a ferment of debate and new thinking – that was one of the reasons, inspired by Jo Grimond, that I joined. Some of our ideas were mad, others were silly and a few were mildly embarrassing. But many, many of the things we pioneered, like green politics (with the Greens), devolution, fair voting, internationalism, gender equality (with Labour), gay rights (without them), sensible drug laws (without me at the time, I am ashamed to say) are now common place and unquestioned in today’s political life. So here is a question. Can you name one big, dangerous idea we Lib Dems have produced since 2015? Vince’s speech of last week began the process of thinking big again. We should pick up his lead and start coming up with our own new, dangerous ideas – and debating them at Conference.

Tomorrow I will suggest four dangerous ideas for starters.

* Paddy Ashdown was the first Leader of the Liberal Democrats from 1988-1999. He is now a Liberal Democrat of the House of Lords