[darrenf]

I would honestly most likely say "triple-one three"!

IME road number† pronunciation in England goes out of its way to avoid "thousand" and "hundred" – with exceptions, of course. Off the top of my head, I reckon I say them like this:

* one or two digits = spoken as the number rather than the digits: A three, M twenty five, etc.

* three digits = sometimes spoken as digits: A two-one-seven - but sometimes broken into two numbers: B one-eleven

* four digits = sometimes the number A thirty-one-hundred (never three-thousand-one-hundred!), sometimes digits B triple-one three, sometimes year-style B thirteen eighteen

There are probably more variations that I can't think of right now too. It's a mess :D

† and bus route numbers, for that matter