The most decisive factor in Saturday’s Calcutta Cup match can be summed up in one word: belief. England have to believe in their blitz defensive system, they have to show confidence in it even when mistakes happen and they have to keep doing that for 80 minutes. Because they can be certain that Finn Russell has belief in bucket-loads and an uncanny ability to move on from mistakes in an instant.

Make no mistake, mastering a brand new defensive system is difficult, all the more so in the middle of a Six Nations championship. I first encountered a blitz defence at Harlequins in 2005 and that was the year we were relegated. There were other factors that contributed but the way that our defence performed was certainly one of them.

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There are so many variables which means it just isn’t something you can perfect overnight. The second time I encountered it was with the British & Irish Lions in 2009 and belief was of paramount importance to its success. You’re getting up high, sometimes you’re ignoring half of the field. Shaun Edwards was the Lions defence coach in 2009 and he created so many drills that gave us edge defenders so much confidence to commit to the system. You have to have belief in what you’re doing. You have to be confident.

In this England side I have seen belief and confidence in their opening two matches. During the first half of the win over Italy, they weren’t great defensively but they were far improved in the second and the biggest difference was more line speed and more aggression. It’s only human nature that if you’re not quite believing in something you can become a bit passive but I see this side becoming more aggressive. There are still mistakes being made, that is inevitable, but I do think this fallow week has come at a critical time for England to iron out as many of them as possible. Having said that, they come up against Russell who is adept at exploiting them.

Russell is someone who actively wants that heat on. He trusts his skill set, you see that in how flat he is, and he wants to pull opposing players out of the line to expose them and exploit their mistakes. He invites a blitz defence and England need to keep in mind that, in the Test arena, against a player of his quality, their line is going to get broken. The most important thing is how they respond. Does it make them become more passive or can they double down?

If we look at the mistakes that England have made defensively, a lot of them are individual errors. Some of them have been through the middle, some have been out wide which has in turn created space in the middle and led to breaks.

The issue is that Russell, above all other fly-halves in the competition, has the ability to force individual errors. He is unpredictable, he has incredible speed of thought and speed of pass. He seduces opponents into defensive reads that aren’t there, he creates mirages.

In that regard it’s going to be a big afternoon for Henry Slade, who has emerged as one of the key defensive leaders in the team, no doubt in part because Exeter employ a similar blitz system. Slade came into the Six Nations in sensational form for Exeter, the perfect response to his omission from the World Cup squad, but he’s had a couple of quiet matches. Part of the problem is that he and Fraser Dingwall have similar strengths, both like to move the ball, but with the return of Ollie Lawrence the division of labour couldn’t be clearer.

Lawrence adds a point of difference to England’s attack and as much as their defensive performance will dictate Saturday’s result, I see a lot of potential for improvement in what they do with the ball and George Furbank can play a big part of that. Freddie Steward is a very tidy player, he was excellent against Wales last time out but the challenge is just different this week.

Furbank is a ball player, he has an extra gear of pace and I think he’s a bit more elusive. When there are a lot of contest kicks there aren’t many better in the world than Steward but Scotland don’t kick to compete a lot, against France they kicked the ball over a mile – they kick long. So if you’re taking out that aerial threat game then what else is Steward bringing? Comparing it to what Furbank can do if it pans out as I hope, Furbank is a bigger attacking threat.

In golf they talk about moving day – the third day of a major – I see this as “moving weekend” for the Six Nations. It’s a critical match and could define each side’s campaign. I’m quietly enjoying how England are progressing through the tournament, the potential is so much more than that of last year’s team. It’ll take another gear change for England to be victorious on Saturday but if they are, don’t write off their championship chances.