Sushdmehta's helpful link relates to companies who are or wish to be directly appointed by UKBA as language test providers. Most of the companies on the existing list are already well-established in the language teaching/testing business:-
http://www.ukba.homeoffice.gov.uk/sitec ... rtners.pdf
Some of these also sub-contract the testing to registered test centres, both in the UK and overseas, and to get established you may find it quicker and easier to approach one of the existing providers with a business plan than to try and get on the UKBA list.
I am a consultant for a company which is a registered test centre in Thailand for one of the UKBA-approved providers. My information from the UK is that some of these providers are telling would-be candidates for the "A1" Speaking and Listening test that they must enrol on a course of up to 40hours before they take the test, and all their courses are full! If someone can converse easily in basic English they don't need any lessons, and our experience is that most of our candidates pass with a bit of guidance beforehand about what the test entails.
