The minimum requirement for single pilot public transport work is 700 hours total with 40 p1 multi IFR. Alotof operators will ask for a 1000TT with a 100 multi.
Centreline Air Charter at Bristol have a concession from the CAA such that they can operate single pilot with 400 hrs total and 40 p1 multi, there may be one or two other operators with a similar concession but that is the only one to my knowledge.