DID they really think they could do this with impunity? Did they really think people wouldn't mind? If so, they've got another think coming. I think it's time to send a blunt message to Scotland's Unionist parties: your efforts to block a referendum on independence are an offence to democracy. And they're going to come back and bite you somewhere tender.

I was speaking to a Labour friend at Westminster recently about moves to reform Scottish devolution. Surely, he said, it wasn't necessary to trouble the public with a referendum in order to bring in a few small changes? I told him there were two things wrong with what he had just said. One, Scotland expected big changes to devolution, not small changes. And two, the only reason he was trying to avoid a vote was his anxiety about keeping independence off the ballot paper.

Labour, the Lib Dems and the Tories are scornful of Alex Salmond's plans to hold a referendum on full sovereignty for Scotland on St Andrew's Day 2010. Their opposition is rich in irony because these parties arguably made such a vote inevitable the moment they signed up to the Calman Commission project to give more powers to Holyrood.

Let me explain. Whatever Calman decides – even at the shallow end of expectations – it will represent a major change in the way our country is run. Democratic precedent requires this change to be put to the Scottish people for ratification. And all common sense and natural justice dictates it's impossible – at this stage in Scotland's history – to have a vote on the constitution without giving the people the option of choosing independence.

Not when support for the SNP is at a historic high.

Not while there is a Nationalist First Minister in Bute House.

And not when there is such a marked split in public opinion on the way forward for the country.

This isn't like 1999, when the Nationalists shelved their ultimate ambitions and joined in a broad coalition for a degree of home rule. Here and now there are two possible routes forward, both with substantial public support. To deny people the chance to state a preference for one of them would only serve to entrench public cynicism about the political classes, and rightly so.

There is an inconvenient truth in Scottish politics that Labour would be foolish to ignore: it's a mistake to think that only SNP supporters back independence. When asked, many dyed-in-the-wool Labour voters also say it is their favoured way forward for Scotland.

There is nothing strange about this – the constitution isn't top of everyone's list of priorities when they decide which party to vote for.

So Labour should be aware that by opposing an independence referendum by fair means or foul they risk further eroding their already diminished support. For a party trying to claw itself back into contention after a bruising election defeat this is a curious way to behave.

Call me paranoid, but I confess I have a niggling worry. It's that Labour's abhorrence of an independence referendum explains its unwillingess (in some quarters of the party at least) to concede any meaningful new powers to Scotland. The brutal logic goes like this: if there are no new powers there's no need for a vote; and if there's no vote there's no way Salmond can squeeze independence onto the ballot; so let's not give Holyrood any more powers.

Scotland's desire to see its democracy mature would thus be stymied by people who cannot countenance the idea of a democratic vote with independence as a legitimate option. It is one thing to believe Scotland should stay within the UK. It is quite another to deny a voice to those on the other side of the argument.

Another point to ponder for the Labour refuseniks is this. It isn't just the nationalists who would be incensed by such a scenario – it would also be Labour supporters who are sincere believers in a stronger form of home rule, within the Union. Resisting the national mood for a far stronger Holyrood will simply drive more natural Labour folk into the welcoming arms of the Nationalists.

Here at Scotland on Sunday as we've been putting together our Scotland's Future project (details on page 13) there has been a sense of genuine enthusiasm about the epoch-making decisions that lie ahead.

There are arguments aplenty to be had – some of them cerebral, some of them speaking to our gut instinct and our sense of belonging.

Our hope is that Scotland can have this conversation while doing justice to its best sense of itself as a nation – inquisitive; intelligent; generous; passionate; open; honest.

It also requires an acceptance on all sides that old arguments have to be looked at afresh in the light of new circumstances.

Consequently, the debate has to be approached with a mind which, if not completely open, has to be slightly ajar.

I'm confident most thinking Scots will rise to this challenge. I'm not as confident about key people in the Labour, Lib Dem and Tory parties.

Surely a good place to start would be accepting that one of the iconic political questions in Scottish politics over the past 40 years – should we be independent? – requires an answer. The attitude of the unionist parties to this key question of a referendum has the capacity to sour the wider debate.