I've paid 1200 PLN{ 235GBP} for a new italian LPG instalation with 45l tank.Complete instalation, tank ,assembly plus adjusting the whole setup on lambda gas analyzer .It was Landi Renzo or Tomasetto I think , here in Poland 3 years ago, though the price hasn't changed since then.I have carb in my car, for spi it would be maby 20-30 GBP more expensive. Panda 4x4 with punto 1242 8v engine consumes 9-10 liters in urban cycle, 7-9 extraurban.{ It is more fuel efficent with 1.2 engine than with original 1.0, more torque , better torque curve}.
I don't know the UK regulations about LPG, Is it allowed to drive to another country , have LPG installed there and make it road legal in UK?