Can you give me just the organization id?
SELECT T1.organisation_id FROM Organisations AS T1 JOIN Research_Staff AS T2 ON T1.organisation_id   =   T2.employer_organisation_id GROUP BY T1.organisation_id ORDER BY count ( * )  DESC LIMIT 1
just the organization id refers to SELECT organisation_id; organization with the highest number of research staff refers to ORDER BY COUNT(*) DESC LIMIT 1;