Hi RedPlume, and welcome.
The fact that this is in red ink is a strong indication that it was written by a checking clerk while the returns were being analysed, rather than anything the householder wrote to indicate nationality. Annotations are quite often seen on census pages, and what you see here, I think, is 240, with the first character being a mistake that's been crossed out.
Numbers in or next to the column showing the birthplace seem to refer to those born in a different county from the one they were enumerated in. I've never seen a list of them, but if you were to find someone else born in Berkshire but enumerated elsewhere, they'd probably have 240 against them as well.
(Occupations were also analysed with number codes, and lists of these are available online. This is quite useful with obscure job titles or bad handwriting.)