I'd aim for a 5-7yr old diesel Superb or Octavia & try to avoid getting a loan. I learned the expensive way that a car will keep going forever as long as you keep the oil topped up
Also, too much uncertainty in the near future (Brexit, Trump, SF/PBP/AAA getting into power) to buy new or spend any sort of money. Apart from things like Brexit, a crash would put you out of business and/or some cnut could steal your taxi and burn it out. Also, lots of stories in the newspapers about people targeting taxis in fake crash scams.
With most of the country driving diesels, they ain't gonna disappear anytime soon. With all the scare stories about them and hipsters buying electric, you should be able to pick up a cheap-ish second-hand one?
I don't get the hybrids anyways. As I understand it, they drive for 40miles or so on electric and then switch back to the 'real' engine. You're paying a lot upfront for the extra weight and 2 engines for those electric miles? And I don't understand how the Prius is legal considering how small the boot is! Can you even fit the weekly shopping in there?