There is in Tom Stoppard’s splendid play Arcadia a small error that has niggled me on every occasion I have seen it, perhaps five or six times since its premiere at the National Theatre in 1993.

I noticed it with irritation at Aylesbury Waterside last week.

Others will possibly spot it next month when the production from English Touring Theatre and Theatre Royal Brighton visits Oxford Playhouse.

Or will they?

The mistake concerns the title of one of the characters and titles are not a subject that most people know much about these days.

I find it hard to believe, though, that someone will not have brought the matter to the playwright's attention of the playwright.

The play, as many will know, is set in a stately home belonging to the Earl and Countess of Croom. We never meet the earl, but the countess is a principal character, somewhat in Lady Bracknell mode.

An important part is played in the drama from the start by the Crooms’ 13-year-old daughter, Lady Thomasina Coverly.

Later we meet her younger brother who is called Lord Augustus Coverly, and referred to as such. This is a name he could not possibly carry.

Stoppard does not make clear if Augustus is Thomasina’s only brother; but if he is, he would be heir to Lord Croom and therefore the holder of a courtesy title (Viscount or Lord something) in which his first name would not figure. If he has an older brother (or brothers) then he would not be a lord at all but merely "the Honourable" and referred to in speech as Mr Coverly.

That earls’ younger sons are not lords, whereas their sisters are all ladies, is one of the inequalities in our system of titles.

Does this matter?

Not much – except that you start to wonder, in a play so concerned with erudite scientific knowledge, whether there is anything else that Stoppard has got wrong.