The November 2007 issue of Insight, the newsletter of the United Kingdom Intellectual Property Office (UK IPO) carries this reminder about the legal status of trade mark protection symbols in the United Kingdom:

When can I use the symbol "TM"?

The symbol "TM" has no legal significance in the United Kingdom, and is therefore free for anybody to use. It is intended to show that you are using your name to trade, but that it is not necessarily registered. You do not have to identify your trade mark as registered.

You can use the ® symbol or the abbreviation "RTM" (for Registered Trade Mark) to show that your trade mark is registered, the mark can be registered somewhere other than in the United Kingdom.

The ® symbol usually is usually placed on the right-hand side of the trade mark, in a smaller type size than the mark itself, and in a raised (superscript) position; none of this is compulsory. If you do not have the ® symbol available, you can use the abbreviation "RTM".

It is a criminal offence to use the ® or the abbreviation "RTM", on a mark that is not registered anywhere in the world".