There is no simple answer to your query as much will depend on size, occupancy and layout of the office. There is I believe an absolute minimum figure of 800mm you can work with, but that's no good if you have mobility impaired or wheelchair users to consider. Final exit route considerations must accord with BS5588. Your Fire Risk Assessor can advise. As you "squeeze" that overall work area and bring more people and equipment in, so you add to problematic issues such as thermal comfort, air quality, nuisance noise, electrical supplies, etc.

Adding to A Kurdziel comments, it should also be noted that 11m3 in reg 11 ACOP (welfare Regs) is a minimum requirement per person and may be insufficient if much of the room is taken up by furniture. Consideration may also be given to legal requirements in reg 12(3) of welfare regs, that increased restriction of access and egress route could lead to an increase of trips risks, as these routes may be at more risk of becoming congested with personal and office items. However I would agree the is no definitive value and it will be based on a "site specific" assessment of those significant risks and fire risks.