"Richard J." typed

See my other post; I think Clive is mistaken. In any case, they
couldn't go straight from 01 to 020 7 because 0207 was already the code
for Consett, Durham (now 01207). Similarly, 0208 was Bodmin, Cornwall.

Ummm... The 1 was inserted in 1995 to all trunk numbers. London numbers
changed from 071 to 0171 etc
London got the 020 prefix _much_ later (?2001)

I've seen quite a few vehicles which even to this day bear phone
numbers such as 01532 xxxxxx or 01734 xxxxxx, having blindly
applied the "insert a 1" rule to codes that changed completely - eg
to 0113 or 0118.

01532 and 01734 were valid dialling codes for several years

I don't know about Leeds, but Reading changed to 01734 in 1995
(phONEday). The new code of 0118 was introduced in 1996, in parallel
with 01734 which was withdrawn in 1998.

--
Helen D. Vecht:
Edgware.