Seminar Room 122 in the Sir Alexander Fleming (SAFB) at Imperial College Campus at South Kensington.
The nearest tube station is South Kensington.
Details of the campus can be found here: http://www.imperial.ac.uk/visit/campuses/south-kensington/
The location of the SAFB can be found on the Campus map: https://www.imperial.ac.uk/media/imperial-college/visit/public/SouthKensingtonCampus.pdf
Upon entering the SAF Building, take the wide stairs in front of you to the mezzanine level and the Seminar Room 122 will be on your right.