As a British citizen can I deliver a training workshop in the USA?

Sure! No problem.

You need a proper visa. If your employer is sending you to US to do a short-term seminar for its US employees, you might just need a business visa - and your employer will get it or provide all the proper documentation. You will, of course, be doing such a thing as part of your ordinary job & paid in your own country by your employer there, same as you would if running the program for your company's employees in UK, EU, or Timbuktoo.

Are you running a training program & have a business of conducting training workshops around the world? People who sign up will be paying you or your own company for the training? Hire an AILA attorney, as you have some serious hurdles to jump to get the proper kind of visa for this.

you may be able to get a visa for such an event if the subject is not available from americans
if its going to be a paid event ... then you need an aila lawyer