One thing is sure. Even if he blocks an independence referendum in the short term, Johnson's actions make independence more likely in the long term. It's a matter of reactance: limiting people's autonomy increases their desire to reassert autonomy when they have the chance.

This is true of any issue and can lead us to act in ways we don't particularly desire in order to show that we can. It is doubly powerful when the issue is independence and an outside agent is limiting one's ability to be independent.

If one wanted to sustain the argument that Scots can't express their own values and priorities as part of the UK, it would be hard to provide more powerful evidence than prohibiting the referendum. So why is Johnson acting in ways that contradict his professed support for Union?