There is no single agreed definition of ‘direct employment in scientific research’ in any of the existing classification systems. Various possibilities present themselves for providing estimates of the numbers employed in scientific research, all with their own advantages and disadvantages.
In prioritising shortage occupations for the immigration points-based system (PBS) the Migration Advisory Committee (MAC) has defined a list of occupations as “PhD level” jobs. These were defined at the 4-digit level within the Standard Occupational Classification (SOC) system, and cover the following eight SOC codes. Note that it includes all jobs in these codes regardless of whether the individuals themselves hold a PhD or not.
1137—Research and Development Managers
2112—Biological Scientists and Research Chemists
2113—Physicists, Geologists and Meteorologists
2311—Higher Education teaching Professionals
2322—Social Science Researchers
2329—Researchers not elsewhere classified.
We have taken the numbers employed in these eight occupations to arrive at the estimate in this answer, using the Annual Population Survey (APS) for 2010. It will include some employees who are probably not ‘directly employed in scientific research’, but equally it will also exclude some employees classified in other occupational groups who are working in scientific research (e.g. laboratory technicians). This will be true for any definition chosen.