Paul Rigg wrote:

I seem to recall that the post office put second class mail up from
4d to 2.5p (ie 6d) and first class mail up from 5d to 3p (7.2d) and
claimed that it wasnt really a price increase.

You are correct about the increase, but I seem to recall that it was
explained by the PO that prices were due to rise at about the same time,
and it would be easier and cheaper to combine the price rise and
decimalisation rather than have two changes.

In the event, as I recall, there was quite a lengthy postal strike over D-
day, so the decimal stamps didn't come into (much) use until some time
later.

(At the time, I was on a student union committee, and we pledged to convert
all our prices at the official conversion rate. We had a complaint that at
the old prices, one scoop of mashed potato was 4d and two scoops were 8d,
but applying official conversion rates, one scoop was now 1.5p and two
scoops were 3.5p.)

Peter

--
Peter Campbell Smith ~ London ~ pjcs00 (a) gmail.com