I bought a brand new Ford Fiesta in 2014 - Titanium five-door, with metallic paint and front and rear parking sensors. From day one, the parking sensors drive me nuts - they go off at random when I'm driving and front and back in unison when I park, but I just thought (having never had them before) that parking sensors were a waste of time and money.

Fast forward two years, and a small black box falls out into the boot. It transpires the dealer put after-market sensors in, rather than getting a car with factory fit OEM sensors as I had ordered and paid for.

They are spliced into the car's electric loom and have been punched through the engine's weatherproof seal. Which explains why they are so rubbish, and why I have none of the functionality detailed in my owner manual... I am furious - it's not what you expect when you buy a new car.

Dealer is offering me £300 cash, or trade in on a new car with me paying £3500 difference. I am not happy with either of these options - in the first, I am still stuck with the rubbish sensors and a car that has been tampered with, and in the second I don't see why I should be out of pocket - up to this point I had no intention of trading the car in.

What would you advise?