because they could be carrying a bomb
A 'green card' grants you official immigrant status in the United States. It has nothing to do with the UK.
No, a UK visa is only valid for the UK. You need a "Schengen visa" for Switzerland.
South Africans require a visa to enter the UK, but it is not a difficult process to get one; just start the process in good time. You may not know that South Africans now require a visa just to transit through a UK airport.
Yes. A UK visa is not a valid Dubai visa
No need for a visa, as the UK is a participant in the Visa Waiver Program.
No A UK visa is only valid for the UK. For most European countries, if you need a visa it will be a so-called 'Schengen visa', which is valid for 29 countries. But the UK is not a member of Schengen.
I once traveled to Switzerland on my UK visa.
No. Northern Ireland is part of the UK, so the visa will cover it.
At this moment in time Botswana Passport holders do not need a Visa to enter the UK. However, this may be subject to change in the near future as South African Nationals have recently been included on the list of nationals needing Visas to enter the UK (March, 2009) and Botswana's requirements are due to be reassessed in September, 2009.
You can establish your own business in the UK if you have the UK work visa.
You will also need a permit to start a business in the UK. You should contact the Pakistani Embassy.
Tier 1 dependent visa's are visa's for family members to stay in or come to the UK. The person they are applying under must have a post-study worker visa in the UK.