He might have been the heir apparent for more than a year but Alastair Cook insisted he'd been taken aback by his elevation to the England Test captaincy following Andrew Strauss's retirement on Wednesday.

Cook insisted he had no idea his Test match opening partner was considering not just giving up the captaincy but quitting all cricket, until told on Tuesday of his fellow left-hander's decision.

Asked if his elevation to the job he'd long been tipped to inherit had come earlier than expected Cook, who replaced Strauss as England's one-day captain following the latter's one-day retirement after last year's World Cup, replied: "Yes I think it has. It's been a bit of a strange 24 hours for me personally."

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"I'm incredibly proud to be sitting here now as captain of England," said the 27-year-old Essex batsman, who scored a century on his Test debut against India in Nagpur in 2006.

"It's a huge honour for me. I'm very excited about the challenge."

Strauss was one of England's most successful Test captains winning 24 of his 50 matches in charge and leading the side to home and away Ashes series wins.

The Middlesex batsman, who took charge in 2009, also guided England to the top of the world Test rankings -- a position they lost to South Africa after the Proteas completed a 51-run win in Strauss's 100th, and as it turned out, last Test at Lord's earlier his month.

"Obviously I've got huge boots to fill following Straussy," said Cook. "He's done an incredible job. Speaking for the players, it was a sad dressing room when we found out.

"I think that speaks volumes for Straussy and what he has done for the side."

If England had an obvious replacement for Strauss as a captain, the question of Cook's opening partner when England play their first Test under their new skipper in India in November is far from clear-cut.

"You take people for granted don't you?," said Cook, who deputised as England Test skipper when Strauss was rested from the 2010 tour of Bangladesh.

"Andrew's played 100 Test matches and scored 7,000 runs. It feels like all my England career I've walked out to bat with him. That's a huge hole to fill and that's a huge compliment to Andrew Strauss."

Cook, who saw England's run of 10 straight wins in completed one-dayers end with Tuesday's 80-run defeat by South Africa in Southampton on Tuesday, added: "We've got India away and we've got two Ashes series in the next 18 months.

"We have got a lot of cricket to play and hopefully I can do a good job."

The closing weeks of Strauss's time as England captain were overshadowed by the controversy surrounding his predecessor Kevin Pietersen, undoubtedly the most talented of England's current batsmen.

Pietersen has been in England exile since the drawn second Test against his native South Africa, despite a brilliant 149 in Leeds, after it was revealed he'd sent "provocative texts" to Proteas players, some of which were alleged to be critical of Strauss.

England have still to get to the bottom of what the messages actually said and so Pietersen remains barred from international duty.

But if he does not return soon, England could find themselves in India with a decidedly coltish-looking top order.

"I've been on the outside for a lot of the saga," said Cook, set to lead England in the third one-dayer at The Oval on Friday. "The issue hasn't changed. Clearly I'll get involved over the coming weeks.

Strauss, asked what advice he had for his successor, replied: "My advice to Alastair is to really savour and enjoy captaining your country and throw yourself into it with everything you've got.

"Manage your time carefully because it is an all-encompassing job at times and have no regrets. I have every confidence that's what Alastair will do. I'm absolutely certain, with the type of person he is, that he will do a great job."