Before making a commercial there are several important considerations.

There are certain standards that are expected in TV advertising.
Advertisements must be legal, decent and honest.

To ensure that your commercial conforms to these standards it is worthwhile viewing the advertising guidance notes.
These can be found at http://www.asa.org.uk/asa/codes/tv_code/tv_codes/

If you intend to use text in your commercial then guidelines can be found at http://www.asa.org.uk/asa/codes/tv_code/Guidance_Notes/Advertising+Guidance+Note+1.htm

It is the responsibility of all broadcasters to ensure advertising transmitted complies with these codes. Clearcast offers a pre-transmission approval service. Clearcast is a specialist body with 2 principle functions:

1) The examination of pre-production scripts.
2) Full clearance of pre-transmission commercials.

Their website is: www.clearcast.co.uk
All commercials must pass through this organisation.