You can also apply to come to the UK as a business visitor if you intend to carry out any of the following 'permitted activities' here:
"are needed by citizens of the following countries: Afghanistan, Bangladesh, Democratic Republic of the Congo (former Zaire), Eritrea, Ethiopia, Ghana, Iran, Iraq, Nigeria, Pakistan, Somalia and Sri Lanka. If you require an airport transit visa, you are permitted to use the international part of the airport during intermediate landing or during a change between two journeys, and without entering the country in question."