From the RAL web site:

“The GIST has been set up as a European group of scientists in order to assist the GERB Principle Investigator in defining the user requirements for the GERB mission and in monitoring the scientific aspects of the programme”

From the EUMETSAT web site:

“The science aspects of the GERB project are monitored by the GIST under the leadership of the Principal Investigator.”

Prof. J. E. Harries of Imperial College London has been acting as GERB Principal Investigator from the very beginning of the project until 2014. In 2014, Helen Brindley took over the PI responsibility.

From GIST-16 onward, the GIST agenda, minutes and presentations are available on the GERB-team site at Imperial College (password is needed): http://www.sp.ph.ic.ac.uk/gerb/gerbteam/gistmeetings

GERB Team (gerb “@” imperial.ac.uk)
Space & Atmospheric Physics Group
Blackett Laboratory
Imperial College
UK