Sorry, couldn't find this designation in Tagg/Wheeler "From Sea To Air", so only thing
that's clear is, that a Flying boat is meant, as the article mentions it in relation to an
automatic mooring system.
I've taken a look again at the Flight article, and I think the SR.56 is actually a mistake. The rest of the article talks about the SR.45; ie the Princess, and I think that was the type that was inferred by the article. As they say, to err is human, but it takes a computer to really foul it up! ( a problem they did not have in 1946!).
I think its just a typo, instead of typing 45 they typed 56. I don't think there is any mystery here, the article at that point is clearly discussing the Princess.
The SR.55 designation is irrelevant as its a much later design, as has already been pointed out in the Saro designation thread you linked to.
There isn't really much point wasting time on chasing for phantoms due to typos, these are so rife in all printed material that we just need to discount those and move on.
if we say it's a misprint from "45" to "56",that's not sense,but we know the series from SR.46
up to SR.53 was missing,except SR.51 & SR.52,which I saw them in a book,not come in my
mind now,we can say it's probably SR.46 ?.
I agree100% with Hood and the others. Why, in an article about the SR45 Princess, would you suddenly change the subject and make one small reference to an undefined project? Also 'development' means a lot more than just being designed, it implies metal being cut.
A simple typo, hit one key to the right on the typewriter and instead of 45 you type 56. I make mistakes like that all the time
They are only a mystery if you believe that they actually existed. We know that Saro projects were in the P series, commencing after WW2 with P100. The few projects that advanced to full design were given an SR number and these are not sequential. I see no reason to assume that SR46 and 56 were full project designs, where did you read this?