Well, according to New Forest District Council who licence both the definition is clear:
"Hackney Carriage Vehicles which are available for hire at a taxi rank and ply for hire in the street. These vehicles are identifiable by a compulsory condition to carry an illuminated roof sign and display a yellow council licence plate on the rear of the vehicle.Private Hire Vehicles which must be pre-booked by telephone or in person will only display a white council licence plate on the rear of the vehicle."
So, there you have it! Exciting huh?! But, still ... if you were thinking to yourself "I need transport to get me from Southampton to Heathrow (or Gatwick, or Luton, Or London, or Brighton ...)" you wouldn't necessarily be thinking "I need a private hire vehicle", more likely you'd be thinking "I need a taxi" - so, here's our dilemma: will you forgive us for calling ourselves a 'taxi service'?!
We do hope so as Jameson Executive Private Hire is a luxurious but affordable way to travel, regardless of not officially being a taxi!