But these days Sheasby is pushing ever closer to the England recognition he craves - to the extent that his club's director of rugby, the former England coach Dick Best, has publicly lambasted Jack Rowell for leaving him out - and so it is time to cast off the image for good.
For Sheasby tomorrow's visit to The Stoop by Leicester, second playing third in the First Division, is therefore as timely as could be. He has ground to make up, having missed out on the England squad for this month's South Africa match and then not figuring among those mentioned when it came to this week's team selection.
But if he keeps proving himself as he has been doing this season he believes he has every hope of elevation, into the squad at any rate, for the subsequent game against Western Samoa. If so, it will have been a while in coming.
Sheasby is one of those back-row forwards you cannot help but notice and he has been playing senior rugby for Quins ever since 1987, yet all his international career amounts to is half-a-dozen appearances for England A and a notable part in the England VII who won the World Cup Sevens in 1993.
"He's someone who is living under a past image: of a sevens player, a bit light-hearted about it all," Keith Richardson, the Harlequins coach, said. "But when you get down to it he plays a very hard game. He wins a lot of ball, is tactically very aware and when he puts his mind to it he can be as effective as anybody in the game."
Yet it is as if Sheasby has to prove himself twice over, not simply in terms of his rugby capabilities but because of that well-spoken public-school refinement (in his case Radley) which is the stuff of Harlequin caricature though hardly modern reality. Not when Jason Leonard, late of Barking, is leading the side.
The truth is people have sometimes thought Quins did not really care and, alas for Sheasby, have thought that of him too. Not guilty, he pleads. "Anyone who knows me, anyone who has played with me, anyone who has coached me knows I am fully committed, 100 per cent fit and dedicated to whatever cause it is.
"I have proved that without a doubt for Harlequins. I've been with them through the rough and smooth, seen Dick Best come and go and, if anyone really did think that way about me, as soon as I play with them or am coached by them they change their opinion."
This is passionate personal pleading but at the same time the determinedly non-dilettante Sheasby does own up to the sin of enjoying himself - partly because of an overwhelming love of the game and partly because he is a good-time type of guy.
"I'm not so serious at every moment of the day that I'm not going to enjoy to the full the wonderful situations rugby creates: the different environments, different cultures and different people one meets along the way. Dinners, partying, beautiful women . . . wherever they occur I will maximise them to the full, just as I do when it comes to training and playing.
"Outside rugby my attitude is happy-go-lucky. As soon as one goes on the field it's work but after that, if there's a laugh to be had or something to be done to lighten the mood and to bring back a sense of reality, you've got to do it in order to keep your sanity."
It is strange indeed to hear such a high-grade rugby player express such sentiments. In this sense Sheasby is a throwback to a kinder age, and the better for it. Rugby union and some rugby players may be going professional but he has no intention of ceasing to be a maths master at Pangbourne College, Berkshire.
That said, ambition has never burned more fiercely within him. Sheasby was told he was close to selection for England's 1995 World Cup squad and, having missed out on South Africa, went instead with England A to Australia, where he further enhanced his reputation.
At 28, he is not the youngest contender but he could put forward long experience as an argument in his favour. There have been two University match appearances for Cambridge, the '93 World Sevens and a consistently impressive showing for Harlequins along the way, and, in haranguing Rowell, Best would promote his man as the model of a creative modern loose forward.
Best accused the England selectors of "having a mental block against him" and Richardson, while needing to tread lightly because of his supplementary coaching position with England A, is willing to forsake strict impartiality by also supporting Sheasby for the earliest advancement.
It leaves Sheasby himself faintly bemused, since he reckons he has been doing what is necessary for years rather than only the past couple of months. He was at the forefront of Quins' desperate struggle against relegation last season and has figured with equal prominence in this season's reversal of fortune.
Indeed you only have to look at Quins' forward travails without him when a gastric upset absented him from the Bath game a fortnight ago, and then note the sharp improvement on his return at Gloucester last Saturday to appreciate his considerable importance.
"Pleased as I may be with my form, I wouldn't say it's any better than it was last season or the season before that," he said. "In fact I would say that last season I had hardly one bad game. The difference is between playing well in a losing side and playing well in a winning side. Somehow, that's what gets you noticed."Reuse content