http://h2zkj5xeycxb2esnyqeabuuo6ui6jlkdb72qjfi2hu3y3h5ilpmjphid.onion/wiki/Visas/index.html
To find out if you need a UK visa, check http://www.ukvisas.gov.uk/ A UK 'visitor' visa is sufficient to attend a conference: you do not need a business visa. Visa process http://www.ukvisas.gov.uk/ gives information for each country, including the information that needs to be provided to apply for a visa, and where it should be sent.