It is the travelers responsibility to check and confirm current visa requirements to enter United Kingdom. You may check with the UK Border Agency whether you need a visa and how to obtain one if necessary.
Requests for Visa Support Letters
For security purposes, the conference has policy for issuing official Visa Support Letters as follows:

Visa Support Letters will be issued only after you have successfully registered and paid for your conference.

Visa Support Letters can only be issued for the person accepted to attend the conference. Unfortunately we cannot issue Visa Support Letters for guests of participants.

Note: Obtaining a Visa Support Letter from Scientific Federation will not guarantee that your U.K. visa application will be approved. The letter is merely supplementary information that explains a visa applicant's intended purpose of travel to United Kingdom.