Four years ago, just before the start of the Ashes series, the Australia wicketkeeper was asked about his habit of “walking” when he had edged the ball behind, even if the umpire had not raised his finger. It was put to Adam Gilchrist that if the series came down to the final Test and Australia needed a few runs to win with one wicket left and he nicked the ball, would he walk even then?

He paused, puffed out his cheeks and then said: “Ah, mate, if those were the circumstances, I wouldn't be nicking it behind in the first place.”

Gilchrist is back in London this week to preach the good word about fair play and sportsmanship before the latest Ashes series. Tonight, he will deliver the MCC's Spirit of Cricket lecture at Lord's, an annual event given in recent years by the likes of Richie Benaud, Archbishop Desmond Tutu and this newspaper's own Christopher Martin-Jenkins.

He says that his talk will be about the challenges facing the game - Twenty20 versus Test cricket and the like - but he is bound to be asked about that curious honesty of his, which was notably seen in the 2003 World Cup semi-final against Sri Lanka when he trotted off even after Rudi Koertzen, the umpire, had shaken his head in reply to an appeal for a catch.

Gilchrist is not an unstereotypical Australian - he plays hard, is fond of a sledge, speaks bluntly - but he has had this moral code since childhood that it is wrong to dupe the umpire.

He said yesterday that there were two instances in his youth that defined his approach. “I came over to England when I was 17 and played for Richmond [in southwest London],” he said. “In one game I was on 80-odd when I got a massive edge but was given not out. I walked off anyway but when I got to the changing room my team-mates asked what I thought I was doing.

“Then, back in Australia in a second XI game for New South Wales, I got a thin edge, didn't walk and went on to make a hundred. I felt so bad afterwards that I went to apologise to the bowler, who was a 38-year-old veteran. He said, ‘Don't worry, this game obviously means more to you than it does to me.' And I thought, ‘Yeah, but still. At what cost?'” From that point, he decided he would always walk if he had hit the ball.

It is not a philosophy that many share. Ricky Ponting, the Australia captain, has said flat out that he does not walk. Gilchrist tried, with little success, to convert other team-mates. “I always felt a little bit of paranoia about what they were saying about me,” he said.

“Generally when I explained to a team-mate that it was about taking responsibility and accountability and that walking would improve umpiring, it was met with silence. I never had one of them go, ‘Yeah.' But no one stood up to me or said I couldn't do it and maybe that was the greatest acknowledgment that I was right.”

Gilchrist believes that this summer's Ashes will, as in 2005, go to the wire. “It's going to be really evenly fought, they are two even teams,” he said, although he backs Ponting to triumph with a relatively inexperienced squad.

“I've been really encouraged by listening to Ponting,” he said. “His enthusiasm is exceptional. He's really got this chance to mould and develop a group of players. He hasn't had the opportunity before.”

He praised the decision of Ponting and several of the other leading players to miss this year's Indian Premier League to recharge their batteries. “It was a fantastic decision,” he said. “It shows that their priority is not only to be the best they can this summer but to prolong their careers.”

A weakness is that Australia lack a convincing spin bowler. “That's the greatest difficulty for the team and always would be once Shane Warne retired,” he said. “Personally, I think we need to play a full-time spin bowler. Nathan Hauritz is here and should be given the opportunity, but I played against Bryce McGain [who played in Australia's most recent Test] last year and was really impressed with him.

“The selectors have shown a lack of confidence in knowing who the right person is. No one has shown the unbelievable results to justify selection.”

Not only do Australia lack top-quality spin bowlers but Gilchrist also voiced caution about their batsmen facing Graeme Swann. “I've been impressed by what I've seen of Swann,” he said. “Spinners have been pretty effective against Australia for a while.”

Just think how more effective they would be if all batsmen walked.

Adam Gilchrist was speaking to promote Sky Sports' exclusively live and high definition coverage of The Ashes