Keep the car on UK plates, insure it in the UK and take it to England once a year for an MOT
That seems like a lot of hassle to me unless you drive to the UK once a year anyway. To do that just for the MOT seems a bit pointless given the time and cost in fuel to do that round-trip.
I agree that a conversion seems pointless too.
I don't understand why people don't just sell their RHDs in the UK and buy an LHD in Poland (or Germany etc..) and save the 140 odd quid on road tax, and a couple of hundred quid on insurance.
RHD is much better from an ergonomics point of view.
Well the ergonomics depends on the car - some cars (e.g. Ferrarri) are designed as LHD and so the RHD versions aren't as comfortable. Some cars as designed as RHD (I believe Toyota amongst others) so you are probably right.
and and also a safety point of view.
I don't see how it can be safe to overtake in an RHD vehicle in Europe. You either have restricted visibility or have you to set up extra mirrors or a camera etc..