The rating of the cable is important too - a 2.5mm core mains lead is required on most UK caravan sites to satisfy IEE regulations [1]; rated to either 20 or 25 Amps (depending on the insulation and grade of copper).

Can I plug a 15 amp device into a 20 amp outlet?

Most household electrical receptacles have a 15-amp rating, but they connect to a 20-amp circuit. You can use a device that has a 15-amp plug with either a 15- or 20-amp receptacle. A 20-amp receptacle is for heavy-duty appliances and power tools, such as air compressors.