Alastair Cook has challenged his young England team to take their chance for a memorable overseas series win in South Africa this winter, but admits that he is travelling with an unsettled and inexperienced batting line-up following the decision to dispense with the veteran Ian Bell.

Speaking at Heathrow Airport ahead of England's departure for their four-Test series, Cook insisted he would not be reading too much into South Africa's comprehensive 3-0 defeat against India, their first away series loss for nine years.

However, he did concede that a victory over the No.1-ranked Test nation in the world, in their own conditions, would rank among his finest achievements of his career. And, he added, since the retirement of a raft of their all-time greatest players, the South Africa side that lines up at Durban on Boxing Day for the first Test will be much changed from the one that Cook himself has yet to beat in a Test series in three previous attempts since 2008.

"When you lose the greats of the game, Graeme Smith, Jacques Kallis, Makhaya Ntini, Mark Boucher … there's always going to be a bit of evolution in a side but trying to replace them is nigh on impossible, especially in one generation," Cook said. "They are certainly a different side to what I have played in the past."

England will arrive in Johannesburg on Friday with plenty of optimism but a fair amount of uncertainty as well. Bell's run drought means that the only guaranteed starter in England's middle order is Joe Root at No. 4, and Cook called on the unfamiliar faces in the batting line-up to make a name for themselves in the coming weeks.

"We haven't quite got a settled top seven, there's no doubt about that," he said. "But with Gary [Ballance] coming back, and Nick [Compton] coming back, they've had a taste of it before, and it's a real opportunity for people to stake their claim."

On the absence of Bell, Cook conceded that it had been a tough decision to drop a player with 118 caps and more than a decade of Test experience. However, he backed his team-mate to capitalise on a rare winter break and come back refreshed in the new year, just as Cook himself had done this time last year, following his sacking as England one-day captain ahead of the World Cup.

"Missing a tour might do Bell the world of good. He's been on pretty much every tour since 2000, whether it's with England Under-19s, the Lions or the full side" Alastair Cook

"I sat in on that selection meeting, it was a fairly long one when you are talking about a player of Ian's class and experience," Cook said. "We will miss his experience but he would be the first to admit he hasn't quite scored the runs over the last couple of years.

"But certainly you might see him score them again," he added. "It's a weird thing, missing a tour might do him the world of good. He's been on pretty much every tour since 2000, whether it's with England Under-19s, the Lions or the full side. So a bit of time away from the game might do him the world of good.

"I look back a year ago, when I was left out of the World Cup. It was disappointing at the time, gutting at the time, but those few months away from the firing line, as it was, away from cricket and a time to be at home, actually gave me a real good understanding and a new lease of life. Hopefully that can be the same for Ian."

At the opposite end of the experience spectrum is Cook's probable opening partner for the Durban Test. The uncapped Alex Hales was last month identified by Trevor Bayliss, England's head coach, as the likely man to replace Moeen Ali at the top of the order and if that is the case, he will become Cook's eighth opening partner since the retirement of Andrew Strauss in 2012.

Hales made his mark in the recent ODI series in the UAE, scoring his maiden 50-over hundred to help England seal an impressive 3-1 series win over Pakistan. That followed on from his hard-hitting hundred against Sri Lanka in the World Twenty20 in Bangladesh two years ago, and despite a quiet home ODI series against Australia in September, Cook believes that his potential new partner has learnt a lot in recent months.

Alastair Cook speaks to the media ahead of England's tour of South Africa Getty Images

"You can't guarantee anyone a first-Test place when you are sitting in a hotel," said Cook. "But judging by the way the selection has gone he's got a great opportunity. We've seen in county cricket that he can go on a run and be destructive. He will have experienced a lot, from not scoring too many runs in the Australia one-day series to really bouncing back and leading in the one-dayers [in the UAE]."

As so often in South Africa, the quality of the fast bowling might prove to be the difference between the teams, and on that count, England begin the tour knowing that Vernon Philander will definitely miss the first two Tests, while Dale Steyn is also struggling with injury and is not yet a certain starter.

With James Anderson and Stuart Broad heading to South Africa with their reputation as a partnership arguably at an all-time high following their heroics in adversity in the UAE, the news that Steven Finn is already battling back from the stress-related foot injury that ruled him out of the Pakistan tour is a major fillip for the squad.

Last week, Finn bowled off his full run-up for the first time since his injury and has been cleared to take part in England Lions' Twenty20 series against Pakistan A.

"He won't be ready to bowl in the first Test, but Steven has made big strides over the last couple of weeks," Cook said. "He's up and running a couple of weeks ahead of what we thought he'd be, and that's really encouraging for him."

"It would mean a huge amount [to beat South Africa]," he added. "That is the challenge we've got ahead of us. Reflecting back to Pakistan, something inside of me says that was an opportunity that we couldn't quite take. I wonder if this is an opportunity we can take.

"The 2-0 in Pakistan hurts me quite a lot as I don't feel we were that far off. But now we've got another chance to win away from home."