Different issues, DM. You are insured to drive in the UK but (strictly speaking) you cannot have the work Taxi displayed on the exterior of your vehicle - similar to here but you often see Dad's Taxi or Mum's Taxi stickers on private cars that are overlooked.
You should, however, read the small print on your policy document. You'll probably find that there's a limit on the amount of time you can spend outside the State and retain cover without informing the insurer. Similarly, extras like windscreen cover, breakdown assistance, etc may not apply.