THE moment that Thursday night’s televised leaders’ debate came alive for me – and perhaps the moment at which the Holyrood election campaign came alive – was when the discussion turned to welfare, and specifically the events which have seen the near implosion of the Tory cabinet at Westminster following the resignation of Iain Duncan Smith.

Duncan Smith resigned, he says, over what he believes were indefensible cuts to benefits for the disabled in George Osborne’s Budget.

Leaving aside that fact that the former Tory leader’s motivations in quitting may have as much if not more to do with his campaigning for a “Brexit” vote in the looming EU referendum, his decision has had political repercussions well beyond Westminster, not least in the actions of Scottish Tory leader Ruth Davidson.

Because, while Duncan Smith may have been the self-styled “quiet man” of British politics during his ill-fated spell as leader, it was Ms Davidson whose silence on the issue of cuts to Personal Independence Payments (PIPs) was deafening in the immediate wake of the Budget.

And while she tried to claim during Thursday’s debate that she had always been against the cuts, the reality is that she only decided to speak out after Duncan Smith’s resignation – on the day of Budget itself, three statements were issued in her name welcoming its proposals, none of which questioned the cuts to disabled benefits.

Why is this significant in terms of the Holyrood campaign? Because this election marks the point at which our national parliament acquires the ability, albeit still limited, to do more than just mitigate Westminster cuts. And because the years since devolution have seen hard-won gains for people across Scotland in policies such as free personal care, free prescriptions and free university education.

All of these things constitute a social contract with the people of Scotland – and the need to protect these gains of devolution in the face of Tory Westminster austerity means that this Holyrood election is the most important since the reintroduction of our national parliament 17 years ago.

Ruth Davidson’s less than straight claims over her stance on the Budget disability cuts betrays a deeper truth, namely that the Scottish Tories, were they ever to be in a position of influencing government policy in Scotland, are still joined hand in glove with their parent party in London and as such would threaten the social contract.

Labour’s credentials on this are no more convincing, because, while they claim to have policies which are anti-austerity, there is nothing progressive about forcing average and low paid workers to carry the burden of Tory cuts.

The tax policy I have set out in recent days, and which the SNP will take into this election, has been carefully thought through, is fair and balanced, and is ultimately the right policy for Scotland.

I have made clear that while I am in principle not opposed to a 50p top rate of tax, there is – quite literally – no point in introducing one if it could actually end up costing the public purse. That is the independent advice I have been given, advice which shows that if only a very small number of top earners decided to move their money from Scotland or shift their income into, for example, capital gains – a tax we don't control – it could cost public services millions of pounds.

That is because, crucially, although we are getting new powers over income tax, we are not getting responsibility for combating tax avoidance – powers which we would have with independence.

However, I have made clear that while we will not raise the top tax rate for the first year in which we have control of the new tax powers, the issue will be kept under review.

In Thursday’s debate the SNP’s tax policies were simultaneously attacked as being both too radical and too timid. I think that that will signal to the vast majority of people that ours is the fair and sensible route which should be followed. And the electorate also know that our plan to ask the better off to pay slightly more than under the Tories’ tax policy is a reasonable one, given the social contract we have developed and the specific gains it has brought people across Scotland.

This nation has come a very long way indeed since our parliament was reconvened in 1999. We are more confident, but are also a fairer and more socially just country as a result of the policies Holyrood has pursued. This election is absolutely vital in protecting and building on that progress.