Shipping price by quantity?

I'm looking for an extension that will work by quantity. For example the shipping costs would be
UK: £1.90 (2 shirts £3.00, 3 Shirts £4.50)
USA & Canada & South America: £4.50 (2 shirts £7.20, 3 Shirts £15.20)
etc etc

I can't seem to find anything, anyone else used or seen something like this?

Item-Based Shipping can do this. If you need additional restrictions (such as on total, weight, volume, or postcode), then Formula-Based Shipping can do multiple criteria at the same time.

Item based Shipping, why didn't I think of searching for this! This will do perfectly, thank you very much.

I have a kind of problem though, I naively stripped out the OC version from the footer on front and back end, is there another way to find out what version I am using?

If you're using a 1.5 version, you'll be fine. 1.5 versions will have a "Design" entry in the "System" menu in the admin panel.