Most attendees will not require a visa to attend the conference in London. Nationals of EEA countries (European Economic Area) and OCT (Overseas Countries and Territories with special links to EU members states) can enter the UK visa free.
Nationals of certain other countries — including but not limited to Argentina, Australia, Brazil, Canada, Israel, Japan, Malaysia, Mexico, New Zealand, Singapore, South Korea, USA — do not require a visa to enter the UK to attend a conference for less than 6 months. However, you may be asked for evidence demonstrating:
- The duration of your stay (e.g. a return flight within 6 months of arrival).
- You are attending the conference (e.g. a confirmation email of registration).
- You are able to support yourself during your stay (e.g. a bank statement or pay slips for the past 6 months).
If you are not eligible to enter the UK visa free to attend the conference, and you wish to enter the conference for a period of less than 6 months to attend the conference (and perhaps tourism or visiting relatives), you must apply for a Standard Visitor visa.