Six Nations: Lewis Moody - Tom Croft's awesome return carries a mobile threat for Welsh Six Nations hopes

Having Owen Farrell fit again at No 10 is vital for England – his performances have been so consistent in this Six Nations. Farrell's return in a white shirt was a certainty today but it is changes in the back rows on both sides that are most eye-catching.

It is awesome to see Tom Croft back in the starting XV and encouraging to see Sam Warburton switched across from seven to six to allow Justin Tipuric back into the Wales side. It makes for an interesting combination for both teams. For Wales there are two natural No 7s, for England two men who have played much of their careers at six. I believe both Stuart Lancaster and Rob Howley have made the right choices.

Many say that Chris Robshaw is not a natural seven but I disagree. For players as good as these it is not difficult to make the switch. There is an impact on your game and it is a different role. At seven there is more foraging for the ball, you get fewer carries but do a lot more tackling. At six you carry a lot more ball and are generally more involved in the line-out. A good six can make a good seven and vice versa.

Robshaw has done a remarkable job, both as player and captain. He does superbly at the breakdown and remains England's best option at openside for the foreseeable future. Croft comes from a different mould than the usual six. You look at sides like South Africa and France and they often like to have a big man at six who does a lot of the ball carrying but Croft is not like that. He has put on a significant amount of weight but he is still quick and athletic and can be used in a line-out with only a one-man lift. He brings a different dynamic to the back row – he is as quick as some backs. It is a joy to see him return. He can be a crucial presence whether it comes to making tackles, carrying, or even fielding cross-field kicks – another potential weapon for England. He is a threat to anybody.

It won't be quite as natural for Warburton to play at six as it would be at seven. It is a little harder going from seven to six because you have a far greater role in the line-out, more of a lifting and jumping role and more line-out calls to learn. It's a different involvement.

Nevertheless, in the absence of Dan Lydiate, switching Warburton across to allow Tipuric to come in at seven is the correct decision. It is one they should have done from the start of the tournament. Bob Dwyer, one of my first coaches at Leicester, used to say he would always rather have two No 7s on the pitch than a six and a seven.

It is good to see Warburton back on form – the fact that he is playing well again can only be good for Wales, and a bad sign for England. His approach has been admirable in that he has lost the captaincy and just gone on doing what he does best.

But this is not a contest that will be settled in one area. This is a game where all 23 players on both sides could have an important part to play. Fitness and fatigue could prove an issue. The Six Nations is a long, tough tournament and can really drain players, not just the games but the intensity of training at this level in between. It is gruelling and I expect Lancaster may well have eased off on the physicality of training this past week.

Use of the bench could prove important – James Haskell is ideally suited to a belated introduction to add extra physicality over the closing quarter. This is the sort of game where guys will run themselves into the ground so knowing when a player has given his all and needs to be replaced will be important.

England must ignore Slam fever and play usual game

So who is going to win?

If this game had opened the championship I would have had little doubt as to the outcome – an England victory. But not any more. It is almost impossible to call.

I saw England beating France, and I thought they had what it took to win in Ireland – Scotland and Italy were always games they expected to win – but this will be different. This is the match I am least sure of England winning.

England should be considered rightful favourites. There are a handful of players remaining from the side that went to Ireland in the same situation two years ago and lost. England haven't always dealt with the pressure of expectation that well in recent years – that win against New Zealand was accompanied by none whatsoever. There is undoubtedly expectation now and the players have to deal with it.

The long-term plan towards 2015 – which is what the Stuart Lancaster project is all about – did not require a Grand Slam this season. Winning the Six Nations, whether with or without the Slam, would be job done. But try telling that to the players.

Whether they will be Grand Slam champions comes down to holding their nerve this weekend. This is a game that may well be settled by one mistake, one slip, or one piece of magic.

If Wales get their backs up then it will be very hard for England. This is a good side that has re-found its confidence since that terrible run of results. It is packed with experience and if they begin well I can see Wales winning by the slimmest of margins, a single penalty from the consistent Leigh Halfpenny. I can't see them winning by seven or more to take the title.

England have limited experience of big encounters, bar those few who played in Dublin two years ago. Problems come in big games when teams lose sight of what they have been doing well. Players feel the pressure. They shrink into their shells. If the players believe in the ability that has got them to this point then I can see England winning.

To win a Grand Slam you have to go to places like Cardiff and get it absolutely right – there is no margin for error. One mistake can settle it. I saw the players after the Italy game and they could not wait to get to Cardiff. The chance to win Slams doesn't come very often. Here comes one and I can't wait for it.

Lewis Moody is a TAG Heuer ambassador