Alastair Cook wary of promoting Joe Root as opener

England captain Alastair Cook said it would be a "risk" promoting Joe Root to open alongside him in the Ashes despite the Yorkshireman's impressive series against New Zealand.

The 22-year-old Root, batting at number five, made his maiden Test hundred as England thrashed New Zealand by 247 runs on his Headingley home ground.

Root, who opens for Yorkshire, was named as England's man-of-the-series by New Zealand coach Mike Hesson on Tuesday after his 104 followed a composed 71 in the hosts' 170-run first Test win at Lord's that set up this 2-0 series victory.

Root's recent form has been in stark contrast to that of Nick Compton, Cook's current opening partner.

Since scoring back-to-back hundreds in England's 0-0 drawn series in New Zealand earlier this year, Compton's next six Test innings have yielded just 54 runs, spread across more than six hours at the crease.

Cook, asked if having Root open in the Ashes would be a risk, replied: "Yes I think it would be. It is an important position in a very big series. You are in the firing line straight away and you want to set a good tone at the top of the order, so yes it is a risk."

Compton, grandson of England batting great Denis, was off the field with a rib injury when England wrapped up victory on Tuesday.

"He went for a scan this (Tuesday) morning. Compo. He will be back playing for Somerset on June 2," Cook said.

At least one of England's current specialist batsmen is set to miss out come the first Test against Australia at Trent Bridge in July should Kevin Pietersen, as expected, recover in time from a knee injury.

"Hopefully he keeps progressing well and he comes back on the field," Cook said of Pietersen.

"It has been brewing for a while that if he comes back then there is going to be a tough decision to make."

But before the Ashes, England have a three-match one-day series with New Zealand starting at Lord's on Friday before, as hosts, they compete in the ICC Champions Trophy one-day tournament.

"There is a long time until the Ashes. A lot of things can change," said Cook, whose second innings 130 at Headingley saw him extend his own England Test century record to 25.

"A lot of important one-day cricket will be played.

"Whether you use the word 'momentum' and whether it makes any difference we will know in a month's time."

Cook did not enforce the follow-on when he had the chance Sunday and was, in the view of some pundits, excessively cautious in not declaring England's second innings until after lunch on Monday.

But in a match that England won by a huge margin despite the whole of Friday's first-day being totally washed out, Cook had a ready-made response.

"I think the result vindicates the decision," the 28-year-old left-hander said.

England off-spinner Graeme Swann, set to be a key bowler in the Ashes, proved his fitness after an elbow operation with a Test-best 10 for 132 at Headingley.

Swann's were the best Test figures by a spinner at Headingley since England's Derek Underwood took 10 for 82 against Australia in 1972 on a pitch affected by Fusarium grass mould.

Cook was delighted by Swann's display, saying: "He was outstanding in this game.

"To get 10 wickets at Headingley for the first time in 40 years is a great achievement. He is a world-class spinner but with operations you never quite know.

"He was put under pressure to win a game on a turning pitch for England and he delivered."