You will only need permission (known as ‘entry clearance’ or ‘a visa’) to come to the UK for a business visit of up to six months if you are a national of the 108 countries that currently require a visa to enter the UK.
The UK government visa information website can help you determine whether you require a visa for the UK.
You can apply for a visa within 3 months of intended date of travel at visa sections at UK embassies, high commissions and consulates and through visa application centres around the world. The visa is valid for 6 months.
If you are a non-visa national, permission to come for up to six months is not needed.