Buy the bits from B&Q it's cheaper than getting a kit off ebay or getting shafted by one of the 4x4 parts suppliers.
But this might be of interest before you fit them.
The Road Vehicle Construction and use 1986 regulation 100, a motor vehicle and all its accessories will at all times be kept in a condition so that no danger is caused to any person in or on a vehicle or on the road:
Just found this bit as well
Section 40A Road Traffic Act 1988 as amended by the Road Traffic Act 1991 states: a person is guilty of an offence if he uses, or causes or permits another to use, a motor vehicle.... on a road when.... the condition of the vehicle..., or of its accessories or equipment.... is such that the use of the motor vehicle.... involves a danger of injury to any person.