AFAIK most countries in EU land require the far/jar23 aircraft to be operated multicrew if flown commercially (for reward) even for cargo ops.
The rules are different through the EU, some countries require it for any turbine acft, others specify the type of operation (commercial flights, commercial being anything which is not private flight, aerial work or instructing).
Spain requires all commercial flights involving cargo or PAX to be operated multicrew, both pilots need to be rated,even VFR flights on a Cessna 172!, the only exception are the scenic flights departing and arriving to the same AD, those can be operated single pilot.
EU land is very heterogeneous in respect to air transport regulations, there is the common rules (former JAA rules, now EASA) and then each country can issue it's own regulations.
The info above is by no means exhaustive, just a vague idea of what is the situation in EU.
If you want to find out the requirements better specify which country you are interested in, and you will probably get a more precise reply.
I know, for example, that under UK regs , at least at some point in time, you could do cargo single pilot, there was a company doing them on a C421, and I happened to meet the pilot at the ATS office when filling a FPL, but I am not familiar with the particular regulations, perhaps somebody from UK or familiar with UK regs will be able to throw some light on the subject.
