Neil Williams wrote:

But what is the principle? It's effectively no different from buying a
book of ten stamps when you only have an immediate need for one, is it?

You are not penalised for buying one stamp on its own instead. The
price of a book of 12 stamps is 12 times the price of one.

The point Chris is trying to make is that like Oyster, it is for
convenience. The only difference is that TfL are offering you a financial
benefit as well as convenience with Oyster whilst the Royal Mail aren't
with stamp books.

--
Phil Richards
London, UK
Home Page: http://www.philrichards1.pwp.blueyonder.co.uk