Thank you for your feedback.
I wouldn't argue against, for e.g., a v10 4 litre petrol engine (or lpg) being the better engine for towing.
However, the problem is , and always has been, ether the prohibitive cost to buy new, and a poor residual value.
So ok buy second hand you say, good idea in theory, but for numerous reasons, not for me.
I have however towed with a turbo petrol, my last car.
This engine towed my van with ease , and at a greater rate of knots than my present Xtrail diesel.
The 1.8 turbo petrol gave max torque from 1950rpm to 4500rpm,not many if any 4 pot diesels will do this.
So I don't agree that turbo petrol engines are not tuned for bottom end torque, that my have been the case in the past, but not today.
The VW group I believe are intending to convert all their engines to turbo power, the benefit being lower emissions.
So in conclusion both my last and present cars do the job of towing my van.
The petrol engine is still the most refined off the two, and if it avoids the higher road tax brackets, and the price differential between the two fuels continues to widened, then my next car could once again be a turbo petrol. Trust me the turbo petrol is every bit as flexible to drive as a diesel.