Well laid out and thoughtful response, Gareth. Many thanks.
This leads me to conclude it's not worth it for me given once I drive back to Spain, I tend to use my 125cc moped that does in excess of 100mpg. Incredible, huh?!
Cost of diesel currently in Spain, inclusive of government subsidy averages €1.60 per litre (approx £1.40 per litre).
Best regards, Ian