Yes, you will need a visa to enter the UK if you are not a citizen of a country that is part of the European Union or European Economic Area.
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. You need a "Schengen visa" for Switzerland.
Yes, Colombians need a visa to travel to the UK.
Yes, UK citizens need a visa to travel to Dubai.
No UK citizens do not need a visa to go to Singapore just like Singaporeans do not need a visa to enter UK
NO, in most cases you do not need a visa to come to the UK for a short visit
Yes, most non-UK citizens need a visa to enter the United Kingdom.
No. Northern Ireland is part of the UK, so the visa will cover it.
yes you need a visa
If you require a UK visa you need to apply to the UK government though the embassy in your country. Jersey is a part of the UK, you do not need a separate visa for Jersey.
Yes
Yes, Americans need a visa to travel to the UK for tourism or business purposes.