He's a good coach but that is as far as I would go, says Charlton, far from impressed by the Real manager's antics

At 75, Sir Bobby Charlton's passion for Manchester United and what is best for the club he adores still flames. As Sir Alex Ferguson prepares to take his side to Manchester City for Sunday's first derby of the season, the gentleman of English football whose career remains the domestic game's high-water mark leaves no doubt over his view of one possible heir to the Scot, José Mourinho.

Coming from Charlton, who is a United director and ambassador and was a kingmaker in Ferguson's appointment during 1986, his take on Mourinho is intriguing in a week that began with Ferguson backing the Real Madrid manager's ability to take charge of United, telling ITV4: "He can manage anywhere, absolutely." For Charlton, who embodies the values of the club better than anyone, Mourinho's antics last season do not befit a United manager.

One of the most uncomfortable entries on an ever-lengthening charge sheet was Mourinho's gouging of the eye of Tito Vilanova, then Barcelona's assistant coach, in the 2011 Spanish Super Cup. "A United manager wouldn't do that," Charlton says. "Mourinho is a really good coach but that's as far as I would go really. He's the manager of Real Madrid and we expect to play them in the Champions League by the end of the season."

When it is put to him that it is difficult to imagine a United manager being allowed to get away with some of Mourinho's behaviour, Charlton says: "You are right. He pontificates too much for my liking. He's a good manager, though."

But Ferguson admires Mourinho. "He doesn't like him too much, though," Charlton shoots back.

What none of the United congregation liked were last season's derby performances. The aggregate score finished 7-1 to City, with Mancini's team leaving Old Trafford in October having routed United 6-1, before winning a crucial encounter in late April with a Vincent Kompany header.

Charlton says: "The 6-1 didn't upset me at all because I could see what was happening. Our defence made a mistake, two mistakes, and it was 2-0. They lost control and went forward trying to put it right. It's a problem with City for us, physically, though. They are a strong, big team and that causes us problems."

How were the aftershocks at the club following the 6-1 defeat? "We knew they were improving their team," Charlton says. "The ownership meant that at least financially they were going to build a good side. How could they not do?"

Despite the United blood that courses through him, could the football man inside appreciate how City won the championship with the campaign's final kick? "It's very difficult to compliment City. But we are not stupid," he says. "They won it. It doesn't matter that it was right at the end of the game. We lost and it was a hard pill to swallow. Yes I have got over it but it took a while and it's been tough."

On whether United have strengthened this season, Charlton says: "Our central defence has suffered. [Nemanja] Vidic is the one who controls everybody at the back. We have missed him but I look at us and I'm quite satisfied. Matt Busby used to say to us that if we were six points off the lead at Christmas we would win the league. Not only are we there before Christmas, but we will get better."

The speculation regarding Mancini's future can make City seem a bit of a circus. "Yes, that sums it up well. It's hard playing in this league. You need togetherness and that's what we have. I don't know if others have it," Charlton says.

United again lead the league as Ferguson does what Ferguson does best: build a fresh side while keeping the present one competing. "He is unique. If I was going out of the trenches he is the one I would want beside me. Nobody else. He has something inside him.

"Every football person in this country wants to do what he will do and what he has done in the past. He is fantastic, he just loves it. On a match day the team sheet comes in and you think: 'Oh, I didn't expect that.' More often than not he has done something – or picked somebody – that you wouldn't expect. Usually it works, too."

The drive that won Charlton 106 England caps, the World Cup, the European Cup, the European footballer of the year award, three league titles and the FA Cup is now directed at the charity he founded in 2008, Find A Better Way.

It funds research into developing technology aimed at greatly reducing the time and cost of removing the world's 110 million landmines. At present rates this would require 1,000 years and a $30bn (£18.6bn) spend.

Trips to Bosnia and Cambodia moved Charlton to action. "A soldier called Scotty Lee in Sarajevo got me interested. He had a patch of ground and was giving kids coaching. At the end he told them what to do if ever they came near a landmine. It is horrific for kids – they're coming up to you, and they've lost limbs and everything."

In Cambodia, he received a demonstration. "I can't tell you how horrific it is when you get close to a load of mines going off. I'm coming back on the plane and I said: 'There must be a better way of doing this.'"

While a major breakthrough in the charity's research may be announced in January, Charlton also feels Cristiano Ronaldo could return to United following his £80m departure for Real in 2009. "He wanted to be the biggest player in the world and didn't think he would get that from Manchester United. He would have, though," Charlton says. "I really haven't given him any thoughts but, who knows, maybe we would one day have the opportunity to get him back?"

Was Charlton a factor in Ronaldo's development? "I used to go in the dressing room but there wasn't much I could tell him. I don't really give players much advice but Alex certainly doesn't ban me from doing it. If I say I may mention something to a particular player he will say: 'Yeah, go on … '"

Charlton's greatest United team has Ferguson as the manager and Roy Keane at their centre. "There are certain players that are talismen and when they go on to a football field they take everybody with them," he says.

"Roy Keane just had that thing. He could change the game with the timing of one tackle. I have played with a large number of good players and have played against many, but when you ask me which would I have liked to play with it's Roy Keane I miss out there."

Since Robin van Persie's £24m summer arrival the Dutchman has become the side's star performer, as Wayne Rooney just begins to move into high gear. The sense from some that Rooney has reached a plateau is not shared by Charlton.

"Somewhere down the line he will really explode, in a good way. At present he seems to have a tiny thing about playing with Van Persie. The two of them maybe aren't gelling as well as everybody would have liked. But Wayne is a great player and he has everything at his fingertips to be the best."

Finally, thoughts turn to England's chances at the 2014 World Cup in Brazil. Charlton, who played in three World Cups, the last of them Mexico 1970, says: "If you look at Brazil and the South Americans – and the advantages they have – then you can't sit here and say it looks like we have a great chance, can you? We have to have some physically strong players to cope out there and I have to say that I'm not hopeful."

Founded by Sir Bobby Charlton, Find A Better Way was established to improve the lives of individuals and communities affected by Landmines. More information at: findabetterway.org.uk