If you can use a 4kw VFD then you have a 3~ mains. A normal 1~VFD have a maximum of 2,2kW.
Thats the maximum, what your 13Amp power socket is capable. The VFD can have more power then the motor, but should be in a similiar power range, 1,5 to 2 * the Motor is ok but not 5 times.