Kevin Pietersen's Book has Tarnished England: Alastair Cook

England captain Alastair Cook said Saturday that one of the team's most successful spells had been "tarnished" by Kevin Pietersen's controversial autobiography.

Pietersen, England's leading all-time run-scorer was effectively sacked -- for reasons that have still to be made clear -- by the England and Wales Cricket Board in February after a team led by Cook returned from a 5-0 Ashes thrashing in Australia.

This week saw Pietersen hit back with the publication of his autobiography and a flurry of interviews where he singled out former coach Andy Flower and England wicketkeeper Matt Prior, whom he accused along with a group of senior bowlers of creating a "bullying" on-field culture, for his harshest criticism.

With the ECB yet to respond to Pietersen's comments, it was left to Cook -- a party to the South Africa-born batsman's international exile -- to defend the environment created by Flower and now retired former England captain Andrew Strauss.

"I am very proud of the era I have played in; to win three Ashes, to become the best side in the world; to play with some great players," opening batsman Cook told the BBC.

"To play under Andrew Strauss, to have played under Andy Flower as coach, I have only got respect for these guys. I do believe that era has been tarnished, and I am sad about that."

Meanwhile, Cook, 29, said what Pietersen characterised as "bullying" was simply a case of "frustration boiling over" at missed chances.

"International cricket is a tough place and as a team you are striving for excellence at all times," Cook said.

"Certainly at some stages those frustrations probably boiled over more than they should have done, but that was only people desperate to succeed and wanting to know the other 10 blokes around them were committed 100 percent to them.

"Did it over-step the mark a couple of times? Possibly, but we addressed those issues -- this is something that always happens in teams.

"It certainly wasn't a 'bullying environment' at all in my eyes."

- Flower respect -

Pietersen accused Zimbabwe batting great Flower of being "contagiously sour", while doing nothing to stop the 'bullying' which he insisted would be dished out to all those not part of Prior's dressing-room clique.

But Cook paid tribute to Flower, who oversaw three Ashes series wins and led England to the top of the International Cricket Council Test rankings, by saying: "I only have respect for him as a man, and as a coach. He was an amazing coach for our side.

"Chatting to some of the guys about it, they feel the same; a lot of the success was down to his drive and determination to make us a tough England side."

Meanwhile Cook expressed the hope Prior would play for England again should he recover from an Achilles injury which sidelined the Sussex gloveman midway through the recent home series with India

"Hopefully if he can get through his really nasty injury, we could see him again in an England shirt," said Cook.

"He has to be remembered as a guy who put his heart and soul on the line for England all the time, and the team was all that mattered to him."

Former England skipper Pietersen did question Cook's "qualifications to be captain" following the Ashes debacle, although Cook was subsequently subjected to far more severe criticism of his leadership skills.

Nevertheless, the ECB have continued to back Cook and he is set to lead England in both their upcoming one-day tour of Sri Lanka and at next year's World Cup in Australia and New Zealand.

"I feel very comfortable now in the England captaincy role, I really feel that I have the support of the lads," Cook said.

"We just can't wait to go to Sri Lanka now and face the challenges ahead over the next 12 months."