Analysis by Paul Cairney

Most of the events over the last three years seem to make a vote for Scottish independence more likely.

Let’s start with the immediate impact of the Brexit vote itself, which seemed like a godsend for almost every aspect of the Yes case. First, it gave a new lease of life to all of the Yes stories that I have heard for as long as I can remember. Only independence can guarantee that we, the people of Scotland, make our own decisions. Whatever way we vote, we get a Tory government. You can’t trust it to look out for us. A government with no legitimacy makes decisions on our behalf, and there is nothing the Scottish Government can do about it. We voted overwhelmingly to stay in the EU and we are being dragged out against our will.

Second, it helped turn around the image of a Scottish independence voter. Then, it was the parochial choice of inward-looking obsessives. Now, it is cosmopolitan. Let’s become independent to play a more positive role in Europe. Independence stops us being ruled by the people determined to turn us into a Little England state which blames immigrants for its problems.

Brexit also boosted the No story. First, Scottish independence is riddled with uncertainty, and we can only be sure that things will go badly for a long time. Independence will produce a major financial deficit. Scotland needs the UK as a trading partner, and as a source of currency stability if it hopes to use Sterling. We now know that these negotiations are not pretty: the EU is not giving way to the UK, and the UK expects Ireland (a country of Scotland’s size and stature) to fall in line with its new rules. Second, no one really knew what a Yes vote would mean. Now, Brexit has shown us that the people making the case for change are making it up as they go along, producing promises they do not intend to keep.

Yet, the big difference is about the image of – and trust in – the people who will tell these stories next time: do they seem honest, reliable, and competent?

On the Yes side is the SNP, which is a highly professional party with a huge membership, very popular leadership, and still enjoying a remarkably strong image of governing competence for a party in government for 12 years and dealing with the legacy of its former leader.

On the No side, it is difficult to find any high-profile politician that could make the case with confidence. Until recently, the obvious choice had been Ruth Davidson. The Scottish Conservatives had become successful by emphasising its competent and reliable leadership and downplaying the party, and campaigning almost exclusively on opposing a second referendum on Scottish independence.

Then, Boris Johnson happened. He overshadowed the Scottish party and its leader, reinforcing the old association between support for constitutional change, and opposition to the Conservatives. His reputation for incompetent buffoonery is damaging to Scottish Conservatives. He is on record as being disrespectful to the Scottish case, and will be under relatively high pressure to "stand up for England" in the way that the SNP has become known as "standing up for Scotland".

Put more simply, the person in charge of telling the SNP not to be so gung-ho, unreasonable, or obsessed with national identity and independence from an external authority, is now Boris Johnson. It is difficult to think of someone more likely to make droves of people vote Yes next time.

• Paul Cairney is a Professor of Politics and Public Policy at the University of Stirling