The record is set for a regular update. Leonard, who has won his haul of caps consecutively, is but a mere strippling at 26 and fellow craggy members of the front row union - in particular Phil Orr, whose 58 matches for Ireland is the world benchmark for props - can only envy the potential number of miles left on the clock. At the moment, things are just ticking along nicely.
Not that this was always the case for Leonard, who has had his fair share of misfortune along the way to overhauling Probyn. When two packs come together to form a modern scrum, the pressure felt in the front row is breathtaking, not to mention downright dangerous, if the body position is incorrect. Leonard knows things can sometimes go horribly wrong.
After the Grand Slam win over Wales in March 1992, Leonard was off work for three months thanks to a neck injury requiring surgery that included a muscle graft. With no tour on England's agenda that summer, though, he could rest and was fit enough to resume unbroken duties in the team when Canada came calling in the autumn. "I had an operation like that and it really brought it home to me that rugby isn't everything. People say I've years of playing ahead of me, but I keep my fingers crossed. You don't look four or five years down the line, you look to the next game."
Leonard, an Essex man, was playing for Barking when selected for England Colts, and he was only 21 and at Saracens when he won the first two of his full caps on the 1990 tour of Argentina. "They wanted to see if there was anyone coming through in the front row and said Paul Rendall could rest that summer. It's all about opportunities and I took mine on that trip.''
Leonard then took another important step in what proved to be the right direction, though as a self-employed builder and joiner at the time, there were those who wondered how he might fit in at Harlequins, the city slickers with traditionally strong public school and Oxbridge connections. He need not have worried as he settled into his new club.
"They were lacking a loose head at the time and I walked into an all- international pack. It did more for my game in one season than it would have done in three or four with Saracens. As a prop forward you can't worry about everyone else's game and at Saracens I was tending to try and help other people, whereas at Quins the players had this wealth of experience."
Those city slickers? "Well, there were a fair few of them at Saracens, but what I would say at the time was that Sarries were very much a family club. But Brian Moore turned up with me and he's not exactly stuck up, and Peter Winterbottom was there from Headingley. I think that stuffy public school myth was blown out of the water years and years ago. I think opposing clubs still like to use it to fuel their hatred of Quins." Then again, the lorry-driver Terry Claxton, one of Leonard's predecessors in the club's front row, had already put in some groundwork. "I think it's fair to say Clax broke the mould and brought them out of the dark ages."
Leonard, meanwhile, has taken up some new lines. "I now work for the Route One fire protection and maintenance company." There is also the newspaper column. "I thought I'd give it a try and it's quite enjoyable, though I'm still sucking in breath straight after the game. I don't think you boys have got to worry about me, maybe just the Rob Andrews and Brian Moores."
Leonard may write himself off as a columnist, but he's certainly not writing off the Scots - and one in particular. Tomorrow he will be packing down against Peter Wright for the first time, which may sound a soft touch. On the 1993 Lions tour of New Zealand, Wright was having such a torrid time at tight head that Leonard was involved in a switch to the other side of the scrum.
"Peter didn't have the best of trips and admitted himself that he had a loss of form out there and he did come in for some terrible stick. A lot of it was quite unjustified because you don't go out on a rugby pitch and not try. But he's now playing very well and I haven't seen him in any trouble in the scrum."
As for the match itself: "It's great for rugby in general. The Scots have nothing to lose and the pressure is on us. You can't tell what is going to happen. They've proved everybody wrong this season. International rugby is always very hard and to win over in France for the first time in donkey's years was superb and it tells you a lot about them. They scared the life out of the French.''
In the meantime: "We've got to be disciplined because, with Gavin Hastings around, any lapse in concentration could cost us three points. Our discipline has been good but like everything about our game at the moment it could still be better. We've played some very good games this season but we've not sustained it for 80 minutes. It's a case of finding that final piece in the jigsaw."
Leonard may be about to celebrate on a personal note, but it's the collective reward of a Grand Slam that really counts in his book. "Before my first international in Argentina Jeff Probyn reminded me I was playing for England, my family, friends, and every player who dreamed of pulling on an England shirt. That's a big responsibility."
As for that record, Probyn sends his regards. "I'm not surprised he's got it. He's one of the world's best props. He's totally committed. He was always willing to listen. I've got a lot of respect for him and I wish him all the best. I'm sure he'll be enjoying a double celebration.'' True front row union.Reuse content