Thank you Brian, for your detailed answer – clearly very much more than just a ‘guess’! In the absence of precise numbers (which I wasn’t expecting), I am certainly persuaded by all your arguments.
The source of the statement, D.A.B. Ronald, ‘
Young Nelsons’, provided no supporting evidence or reference. I must admit also that since posting this query, I have come across other assertions that somewhat undermine my confidence in the book, such as that at Trafalgar
‘Nelson had at his disposal the full might of the Channel Fleet, comprising in all 84 ships of the line and frigates’. He also describes the build up of the blockading fleet at Cadiz as the
‘remorseless build up of Britain’s Home Fleet in the Channel’ 
. Elsewhere he implies that William Pitt took the decision to resume war with France in 1803, he refers to Nelson’s band of brothers at the Battle of the Nile as a
‘makeshift squadron Nelson had somehow cobbled together into the semblance of a fighting unit’ 
, and he states categorically that the practice of ‘starting’ men was one and the same thing as the punishment of ‘running the gauntlet’!
Hmm… Maybe I'm over-critical, but we can’t let some of that pass without challenge, can we?