Currency in invoices

[Paddy Walker]

I am migrating from QuickBooks to Gnucash 2.2.6 run under Ubuntu 8.10.
I now have changed my locale to GBP (British pound). I have deleted USD
within Ubuntu. "Choose" within Preferences/Accounts likewise shows GBP
(British pound).Preferences/Reports likewise stipulates GBP (British
pound0
The summary line at the bottom of accounts now uses £ rather than GBP.
Invoice currency has changed from $ to USD but I cannot cahnge it to £
or GBP. Where have I slipped up.
Paddy Walker, Norwich, UK.