"The way England are playing is impressive, but you never know what the Irish are going to do." So spoke the great rugby sage Spike Milligan in the programme for the 1998 match at Twickenham that ushered a then teenaged Jonny Wilkinson on to the international stage. Wilkinson was back in south-west London this week to whip up interest in volunteering as rugby's equivalent of Games Makers at next year's World Cup. And ahead of Saturday's pivotal meeting between England and Ireland in the Six Nations' Championship, the pre-Twickenham talk was much the same, but for different reasons.

"I really like the way England are playing at the moment," said Wilkinson, who was present at the two-point loss in France a fortnight ago which was followed by a 20-0 win in Scotland, while Ireland beat the Scots and Wales with points to spare.

"The whole thing looks solid and professional," he added. "I'm looking at every player and they seem to know where they're supposed to be and what they're supposed to do when they get there. Not playing like robots, but having A and B options and doing it damned well."

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The Irish are difficult to read, not because their results make no sense, as the late Milligan referred to, but because last week's subjugation of Wales's defending champions confounded everyone who pigeon-holed their coach, Joe Schmidt, as wedded to creative rugby and insisting on every player being able to pass.

Ireland made big tackles, drove hard in the maul and deployed their lavishly talented Lions fly-half Jonny Sexton mainly to belt the ball downfield. "Ireland have got that fire of the Grand Slam possibility, when every game is do or die," said Wilkinson. "England know if they beat Ireland they might win the tournament. And they are at home.

"If England are serious about their own World Cup next year, they've got to put a marker down in this game that says, 'This is where we belong, and here we don't lose'."

Wilkinson won the Slam once, in Dublin in 2003. He has begun coaching at his club, Toulon, in preparation for his retirement from playing, and in Paris he caught up with his former team-mates, now England's backs coaches, Andy Farrell and Mike Catt. Midfielders all, and what an area of influence it will be next Saturday.

"Sexton's a huge competitor," said Wilkinson. "When I've played against him, you can hear him – he's never happy, he demands a huge amount of everyone around him, and is a massive leader in that Irish team, more so now that guys like Brian O'Driscoll are getting to the latter stage of their careers. Sexton is in an amazing position, in great form.

Of Sexton's opposite number in the England ranks, Owen Farrell, the former No 10 said: "He is younger, and he's building into that role. He's had a hard journey to begin with, under a huge amount of scrutiny over who should be starting. He's dealt with that enormously well, and not only that but he's done the kicking and never let himself down in that respect. Hopefully now he's benefiting from having a structure in place where he can say, 'I'll do this, then this' rather than full-frontal panic."

But there is caution in Wilkinson's assessment. "Owen has young backs around him and there's no one there, I think, who's able to tell him, 'This is what we're doing'. When I joined that England team at 18, I had Jeremy Guscott, Mike Catt, Paul Grayson and Matt Dawson. I'd make decisions and they'd say, 'No, we're not doing that', and I'd say, 'Fine'. At his age [Farrell turned 22 earlier this month], that's a hell of a responsibility.

"I remember facing New Zealand at Twickenham in 2009 [aged 30 and with 72 caps]. I was edgy about it but I told myself I didn't have the right to feel like that because there were younger guys in that team looking to me. So I made it my inspiration to say, 'Follow me, I'll make the decisions'. Owen has had to say, 'I don't have the right to be nervous', even though he is. That's tricky. I'm admiring it because his mental toughness is beyond where I was at that age, to say, 'Sod it, let's get on with it'."

The rugby-loving Milligan's approach to wing play was based on evasion: "If a 16st player was about to catch me I usually tried to knock on or step into touch." Now, with England's Luther Burrell and Billy Twelvetrees around, that 16st player can be a centre.

Ireland's O'Driscoll and Gordon D'Arcy are not of the same monstrous dimensions but they are the world's most capped centre partnership, and against Wales they were focused, unflashy and dominant.

"Twelvetrees is Mike Catt-ish," said Wilkinson, "he's knocked about at No 10 and will know what Owen Farrell is going through. He can say to Owen, 'Just give this one to me' or 'You go right, I'll go left', as Catty used to do for me. Twelvetrees can also smash the ball up.

"Then you've got your athletes outside, your Burrells. He is going to take defenders off you because he's got footwork, he's got strength, he's got a handoff, he's got ability to crash through tackles.

"The key there is experience. The danger for England lacking experience is a lack of cohesion. O'Driscoll and D'Arcy have seen every eventuality on a rugby field. England have to make up that difference by understanding of the gameplan, talking to each other and sticking together. There's no reason why that England midfield shouldn't go in thinking, 'Why are they going to break us?'

"Ireland have a lot of belief and passion and drive, and I've felt the full wrath of that in the past, when it doesn't matter how structured you are, if these guys keep running at you, eventually you're going to go backwards. It's almost beyond human.

"England need to maintain their understanding and discipline but get close to matching Ireland's passion and ferocity. They need to fire it up to meet the Irish guys head on, to even out that playing field – then match gameplan for gameplan."

Key contests at Twickenham

Mark McCall was a centre for Ireland in the 1990s and played twice against England at Twickenham. Now director of rugby at Saracens, who have six players in the England squad for next week's match, he picks the key areas of confrontation:

Forwards

It all flows from this. Ireland's pack haven't come up against anything like England's yet. Ireland won't be able to maul them like they did against Wales. The English have six top ball-carriers. Their set-piece needs to improve, and probably will.

Tackling

Ireland this season rely less on the choke tackle. They're going lower. If you choke-tackle a big guy like Luther Burrell and get it wrong you find yourself five metres behind the gainline. They will chop-tackle the big men early and get over the ball.

Defence

England's defence is the best. The more ball Scotland had, the worse it got for them. But Joe Schmidt's too clever for that to happen. Ireland have a variety which won't allow England just to come off the line and smash Ireland behind the gainline.

Kicking game

Schmidt's so clever; nobody saw what was coming against Wales. If England drop players back to counteract a kicking game Brian O'Driscoll, Gordon D'Arcy and Johnny Sexton will put the ball into different channels where there are weaknesses. Either way, Jonny May's positioning will be tested.

Generating momentum

If England have to play with average set-piece ball, and play off three-second rucks, do Billy Twelvetrees and Burrell have the nous and experience to do what D'Arcy and O'Driscoll can do? D'Arcy gets over the gainline with brilliant footwork, O'Driscoll is a master kicker.

X-Factor

Peter O'Mahony is storming but Ireland have lost a game-changer in Sean O'Brien. Remember that try in France, when Billy Vunipola got the ball back in two hands after a hand-off and then made the right pass? It was phenomenal skill. He is a game-changer – if he's on the front foot.