Copy from OM pt.A which is most likely a direct or paraphrased version of the regs (to show the requirement MJ is talking about):
The Operator shall ensure that a Commercial Pilot Licence (CPL) holder shall not operate as a commander of an aircraft certified in the AFM for single pilot operations unless:
1. When conducting passenger carrying operations under VFR rules outside a radius of 50 nm from an aerodrome of departure, the pilot has a minimum of 500 hours total flight time on aircraft or holds a valid instrument rating; or
2. When operating on a multi-engine type under Instrument Flight rules (IFR), the pilot has a minimum of
700 hours total flight time on aircraft which includes;
400 hours as pilot-in-command (in accordance with JAR-FCL)
of which 100 hours have been under IFR, including
40 hours multi-engine operation
Note 1 The 400 hours as pilot-in-command may be substituted by hours operating as co-pilot on the basis of two hours as co-pilot is equivalent to one hour as pilot-in-command, provided those hours were gained within an established multi-crew system.