In message , chris French
writes

Postcomm list addresses for complaints for all licensed postal
operators.

http://www.psc.gov.uk/postal-licence...-complain.html

For Royal Mail it gives:

Royal Mail Customer Services
FREEPOST
20 Turner Road
St Rollox Business & Retail Park
Glasgow
G21 1AA

Interesting. The Royal Mail booklet Mail Made Easy gives :

Royal Mail Customer Services
Freepost
PO Box 740
Plymouth
P19 7YB

Another RM booklet, Keeping Our Promise, shows the Glasgow address,
above.
--
Graeme