Cylinder barrels? In a Mini?
Errm, yup he's right. It's nothing to do with the design of the car being innappropriate for the British weather it's due to you driving through a flood. The MINI is not an off road car, it has no published wading depth and should not be driven underwater. Surely everybody knows not to drive through excessively deep water? If you are very lucky the water will have either been detected by the injection system or simply shorted it out and shut the engine down before it got anywhere important. If you have managed to turn it over since that hapened however you will probably have done the same damage as would have happened if water got inside in the first place. As lil dan says, you may well have a hydrauliced engine which will render the entire power unit (possibly even including the gearbox as a friend of mine did to his BMW once) scrap.
Ah, no I just read your blurb and noticed it's a diesel. There is very little chance that any kind of shorting out occured in a diesel engine. The high compression of a diesel would make any water ingress exceedingly bad indeed, that's partly why they have water seperators in the fuel system. I'm afraid to say that your engine is very probably scrap and with the cost of replacing that and everything else the water will have damaged in the engine bay I wouldn't hold out much hope of getting your car back once the insurers are involved, especially with all the claims they will be getting in that area this week due to the floods. Still they might choose to resurrect it, my friend who destroyed his BMW in a similar way got it backeventually and they even had to replace the entire interior in that case. It had a tide line on the headlamps evey morning after that.