"It was part of the grieving process," Andrew Strauss says in his considered but booming voice over tea and biscuits on an autumnal afternoon in Hertfordshire. He might still be cold after a rainy round of golf but it does not take the former England captain long to shake off the polite niceties of a few gentle warm-up questions as he cuts to the heart of loss and painful endings. Strauss is far too grounded to linger over any comparison between death and his retirement from cricket but it is still striking how open he is about his turbulent emotions when he wrote to England's players in August to explain, in personal letters, why he could no longer continue as their captain.

Strauss takes another sip of tea as he remembers that poignant day. "One of the things I've found hardest about retiring was sitting down and writing to those players. It dawned upon me how much like a second family the England team has been to me in recent years. You spend so much time together – probably sharing more nights with them than your wife. It's hard to let go. And as soon as you do let go they move on for the next tour. They're still in that bubble and you're on the other side. Your relationship with those players will never be the same again. I was prepared for that but it was still emotional writing and saying: 'This is it. Fine, I'm off. Goodbye.'"

Of course Strauss is too thoughtful to have scribbled such a cursory farewell. Every letter would have been packed with personal meaning from him to each specific player – summed up by the impressively old-fashioned fact that, rather than texting or emailing, he put pen to paper. "Well," Strauss smiles, "it just proved to me how successfully I'd managed to avoid getting a proper job because my hand was cramping after about 10 minutes. It took me a lot longer than I expected. I wrote the letters on the back of each other and it took at least half a day."

How did he decide who he would write to first – or did he simply move down the batting order? "It was a bit higgledy-piggledy. I had a list and some were easier to write than others and I went first with the ones that I figured would be easier. The ones that were harder to write were those with more emotion attached to them."

Did Kevin Pietersen feature on his list? "Um … I didn't write to KP, actually," he says of Pietersen, whose text messages to his South African friends in the opposition dressing room apparently undermined Strauss during the second Test of an unhappy series for England. "But the main reason was that I wrote all those letters so they could be taken down to the Rose Bowl where the guys were playing [in a one-day international – a form of cricket from which Pietersen had temporarily retired in order to pursue a more lucrative career in the Indian Premier League.] Obviously I texted KP."

A text to Pietersen was probably more appropriate than a beautifully-written letter? "Well yeah," Strauss shrugs. "That was a strange time for the two of us. A lot had happened and during that period we were quite estranged from each other."

Surely that estrangement, between Pietersen and the entire squad, cannot be healed – even though, after an awkward series of meetings, he will play for England against India next month? "It's an interesting point. Maybe it actually makes it easier for the team that I'm not there because some of it was directed to me. It would have been harder if I'd stayed."

Strauss has previously been resolute in stressing that he did not retire because of Pietersen's texts. Is he now saying something different? "No, because of what happened with KP I felt guilty not sorting it before I left. I didn't want to leave it on [the team director] Andy Flower's plate and I felt uncomfortable with Cooky [Alastair Cook] having to deal with it as one of his first tasks. But that would have been the wrong reason for me to stay. I had to go."

Was Strauss aware of Pietersen's soured mood towards him? "Not really. That's the strange thing about it. We knew that Kevin was having issues about the IPL. He retired from one-day cricket and didn't seem happy because it was clear that he was keen to commit to the IPL. But as players we were outside of that. So when it came to a head we were all quite surprised."

It's easy to imagine that Pietersen, being such a willful maverick, has always been difficult to captain. "Well, what makes people like KP special as cricketers is they are different. Nine-tenths of my time as England captain I found him a good guy to have in my team. He set the right example in practice and I felt he could have been far more resentful of me in the sense that he had been removed as captain before I took over. But he just got on with his job and our relationship was pretty good – which is why it was so surprising and baffling when I heard what had been going on. In the preceding months he had not given me any hint of what he thought about me."

Strauss says that he and Pietersen have since met – and he acknowledges that some of England's players have not been blameless in the breakdown of relationships with their star batsman. "I don't think anyone got to the bottom of the text messaging saga. But Kevin has since come up to me and apologised for it and I respect that. He seemed contrite and I think he was sincere. Looking back I think it was wrong some of our players were following that [spoof KP Genius] Twitter account. But I still don't think it's a justification for what Kevin did."

Can Pietersen change perceptions of himself? "It would be fantastic if Kevin does recommit himself to English cricket at a greater level. But if, deep down, he still feels more loyalty to his IPL franchise then obviously it's going to be difficult for him."

Does Strauss believe Pietersen is badly advised – as he released his YouTube pitch at reconciliation in the midst of a fevered night at the London Olympics? "I don't know. But I believe we all have to take responsibilities for our own actions. It was a fraught time for everyone and I now believe that KP is very contrite."

The difficulties for Flower, who is just as straight and disciplined a man as Strauss, will be obvious in India as he tries to ease Pietersen's reintegration. "It will be difficult," Strauss concedes. "One of the problems is that there are two separate sections. One is going on in meeting rooms between KP and the players and on the other side is this media intrigue. From Andy's point of view, they need to get that first part right. If everyone is happy in the dressing room they will play well. But if it's not resolved then it is a problem. I honestly think it's a real problem."

Is reconciliation achievable? "Um … I think that it can be. But everyone has to desperately want it to happen and they all need to let bygones be bygones and not have any grudges and bitterness. Everyone has to want to move forward for the right reasons. That's the question mark and so it's hard for me to tell. But it saddens me that we've been through this – after all the hard work we put in as a group for three-and-a-half years. We all genuinely believed in this special bond and chemistry we had. Unfortunately we've slipped from there and the guys are going to need to recover that. It's going to be tough.

"If they can make it work then obviously England will be a better side with KP in it because he's an outstanding player. But if, behind the scenes, things are difficult and resentment is harboured, and if KP is not fully committed to England, there are going to be problems. But it's in everyone's interests to make it work."

Strauss is not being disingenuous in deflecting any suspicion that he retired simply because of Pietersen. Instead, he offers some touching insights into his slow decline as a Test batsman. "I had noticed signs that my batting was going backwards. I was starting to feel a bit old and that's not a good place to be as a professional athlete. I first felt it 12 months ago. I didn't have a great summer in 2011 and then over the winter I didn't play particularly well. I had a bit of a resurgence against West Indies but I felt like I was swimming against the tide.

"If I'm brutally honest, by the time we reached world No1 I had ticked off everything I'd wanted to achieve. It's then hard to keep yourself hungry and motivated as captain. I also wasn't as mobile in the field. My agility was dropping. One of my favourite shots – the pull – was one I wasn't playing very often and I couldn't work out why. So maybe my reactions were slowing down. I loved captaining and trying to win games – but I wasn't enjoying batting any more."

Strauss nods at the suggestion that, as a great sportsman, it must be immensely painful to lose your ability and desire. "It is. There's this nagging feeling at the back of your mind and you redouble your efforts and work harder as a way of masking that feeling. But it's still there in the background. Every time you don't score runs or you dive for a ball and it just evades you, it creeps back. It's one of those things that when it catches hold of you it's just like a cancer – it spreads."

Could he discuss his feelings with Flower? "It's not something you can talk about. You spend most of your time fighting it. I only spoke to my wife and 12 months ago I marked out the South Africa series as a watershed. If we [England] were playing well and I was batting well that would give me the green light to go on for the [2013] Ashes. But if either of us was not playing well it would be a good time to think about going. In truth, England had taken a step back over the last nine months and I wasn't playing well. It became pretty clear in my mind."

England dipped just as Strauss suffered his personal crisis of confidence. Were his players similarly drained of energy? "We struggled with knowing our next goal. We never quite worked that out. If you say we want to stay No1 for the next 12 months then by definition you're just trying to hold on. I now think that as soon as we beat India to become No1 we should have made a conscious effort to refresh everything. But it's hard to do that when everything seems to be working so well."

Flower once said that he wanted to create a dominant legacy that could rival great teams from the West Indies and Australia. "We discussed it but it was just too big an aim at first. We needed something smaller than that and that's when it becomes trickier. Maybe we could have thought about getting to a certain number of ranking points. Human nature is that when you attain a goal you allow yourself to be happy and content and those emotions are not good in international sport. You have to be unhappy and keep pushing and straining because the opposition will do that."

Who does Strauss believe should replace him as Test opener? "I've heard a lot of good things about Joe Root but it would be hard to say he's the man when I haven't really seen him bat. I've known Nick Compton a long time. He's a fully-formed cricketer and he's scored lots of runs. He probably feels ready to open the batting for England. If KP is back then you have the option of pushing Jonathan Trott up the order. But he's done so well at No3 it seems wrong to swap him round. If it was up to me I would keep Trott at three."

And that would leave Compton to open the batting with Cook? "Nick has always been very good technically. I played with him at Middlesex years ago. He's quite an intense character and determined to make the most of his ability. I don't think he'd be overawed. Andy and Cooky will be looking very closely to see how Compton and Root play in the warm-up games and how they adapt to the squad. Sometimes it's how people hold themselves off the pitch that matters most."

No one in the recent annals of English cricket has conducted himself more admirably both on and off the field than Strauss. England will miss him sorely, both for the batsman he once was and the tough and intelligent captain who steered them to back-to-back Ashes victories and led them to becoming the best Test team in world cricket. He now feels that he is "on gardening leave" as he works out what he might do next.

"I'm not going to make any decisions until after Christmas. It's going to be one of four things and quite possibly a combination of media work, cricket administration, corporate speaking and getting involved in a business unrelated to cricket."

Strauss seems most passionate about safeguarding the Test arena – which is an aim that he can begin to develop as a member of the ICC's cricket committee. "It's a way of dipping my toe into the water and learning more about the ICC and the corporate governance of cricket. I really want to see cricket flourish and I have concerns that we're putting the game under a lot of pressure.

"My biggest concern is that Test cricket and Twenty20 cricket are competing too much. They should be complementing each other and the more they clash the more damaging it will be for cricket. We have to find a way to get the two forms of the game co-existing – and that involves administrators sitting down and banging their heads together and working out a framework. I understand the politics but I'm more interested in what's best for the game."

Strauss seems eminently suited to pursuing a noble cause on behalf of Test cricket. It surely also means he won't be following Michael Vaughan on to Strictly Come Dancing? Strauss pulls a face, perhaps imagining a light entertainment show more geared to Pietersen, and then laughs. "Definitely not! At the risk of sounding like Steve Redgrave when he said 'Shoot me if I get in a boat again', I'll be very disappointed if I end up doing that."

Andrew Strauss is an ambassador for pensions and investment group MetLife (www.metlife.co.uk)