The 25-year-old moves into the No. 10 shirt at the expense of Stephen Jones, who drops to the bench, having also played at full-back and centre in this year’s tournament.

Hook started at centre in the win over Italy last time out but with Jonathan Davies fit to return alongside Jamie Roberts in midfield the Ospreys star is back in his preferred position.

Cardiff Blues winger Leigh Halfpenny gets his first start since last June with Morgan Stoddart, who had been a doubt with a shoulder problem, forced to settle for a place on the bench.

Gatland has resisted the temptation to recall Adam Jones to his unchanged pack while hooker Richard Hibbard has been passed fit to take his place on the bench.

There’s still doubt over the fitness of Jonathan Thomas so a final decision will be made on Thursday of which two of Thomas, Rob McKusker and Andy Powell take their places on the bench.

“This is a crucial game for us as a win will keep us in the Championship mix and take us into that final round with everything still to play for,”said head coach Gatland.

“But it is also a big game for Ireland who are in a similar position to us going into this match.”

15 – Lee Byrne (Ospreys)
14 – Leigh Halfpenny (Blues)
13 – Jamie Roberts (Blues)
12 – Jonathan Davies (Scarlets)
11 – Shane Williams (Ospreys)
10 – James Hook (Ospreys)
9 – Mike Phillips (Ospreys)
1 – Paul James (Ospreys)
2 – Matthew Rees (Scarlets)
3 – Craig Mitchell (Ospreys)
4 – Bradley Davies (Blues)
5 – Alun Wyn Jones (Ospreys)
6 – Dan Lydiate (Dragons)
7 – Sam Warburton (Blues)
8 – Ryan Jones (Ospreys)

Replacements:
16 – Richard Hibbard (Ospreys)
17 - John Yapp (Blues)
18 – TBC two from Rob McCusker (Scarlets), Andy Powell (London Wasps), Jonathan Thomas (Ospreys)
19 – TBC two from Rob McCusker (Scarlets), Andy Powell (London Wasps), Jonathan Thomas (Ospreys)
20 – Dwayne Peel ( Sale Sharks)
21 – Stephen Jones (Scarlets)
22 – Morgan Stoddart (Scarlets)