As you rightly say, Outcome 8.5 of the SRA Code of Conduct, which came into effect on 6 October 2011, requires firms to put "Authorised and regulated by the Solicitors Regulation Authority" on their letterhead, website and emails.
This is an important change in signalling to clients and consumers generally that all firms are not simply regulated by the SRA, but have been subject to an authorisation process to enable them to enter the regulated community and provide legal services to the public. Under risk-based, outcomes-focused regulation, the authorisation process will play a more important role in the regulatory system and the SRA will be applying a greater proportion of its resources to this activity.
The above requirement in Outcome 8.5 applies from 6 October, and firms should have made the necessary changes by this date. Websites must therefore have been amended by this date, along with letterheads printed individually by computer system macros and email footers. However, we recognise that some firms may have existing stocks of pre-printed notepaper and wish to make the change at the point at which new stocks are ordered. We are happy for firms to take this approach provided that the change is made as soon as practicable in the next few months.