If they have a Commercial Licence (and for this purpose, an Instrument Rating - if it's a turbine mirage also a type rating, not required for a piston engined aircraft), issued from the state of registration of the aeroplane, and you let everybody you give a lift to (family / friends / etc.) have those flights for free - you don't charge them: yes, not a problem.
Charge them, use a pilot with only a PPL, no - that's a problem.
To avoid a bunch of trouble, if you're British, it's best to buy a G (British) registered aeroplane, and hire somebody with British licences. You'll want them to have a CPL/IR. There are workarounds for different states of licence and registry, etc. but frankly, you shouldn't need to deal with them, so why bother. That said, many people do this with an N-reg (American) aeroplane and there are plenty of FAA licenced pilots around: but you need to own it through a US based trust. Lots of advice on the interweb about that (and no type rating needed if it's FAA, due different rules.)
G