Assuming you meant 'a leave to enter visa' - it's a document issued separate to a persons passport, granting the passport holder permission to legally enter the UK. IT IS NOT, however permission to stay here indefinitely. If you stay beyond the expiry date, your details will be circulated on the Police National Computer as an absconder.
No, individuals with a Schengen visa cannot enter the UK. The UK is not part of the Schengen Area, so a separate visa is required to enter the UK.
Yes
No need for a visa, as the UK is a participant in the Visa Waiver Program.
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
No UK citizens do not need a visa to go to Singapore just like Singaporeans do not need a visa to enter UK
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 - you still need a visa to enter the UK !
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.
no
No you may not