Many Business English teachers come into the field with either general English teaching backgrounds and/or business experience. In addition to in-service training offered by their own institutions, teachers can attend Business English courses for teachers in the UK and elsewhere. 

For a list of short courses for Business English teachers provided in the UK go to: www.educationuk.org. From the drop down Your Study Options menu, choose Study English in the UK. Then choose Courses for Teachers under Types of Course. Using the Key Word search function can narrow your options.

The LCCI's ( London Chamber of Commerce and Industry) Further Certificate for Teachers of Business English is designed for qualified teachers of general English who wish to gain a supplementary specialist teaching qualification in English for business purposes.
(http://www.lccieb.com/Web/lccieb/businessenglish.aspx?sid=1)

English UK and Trinity College London have recently developed the Certificate in International Business English Teaching (Cert. IBET), which will assess practical business English teaching awareness and application (www.trinitycollegelondon.co.uk).