Although Design With Campers In Mind,

this handy 'washing machine' might come in useful if the predicted power cuts arrive,

it is simplicity itself, created by Japanese company Kao, the Attack Zero laundry bag is a 5-liter zipper bag designed to help do your laundry on the go or when there is no electricity, all you have to do is open the zipper lock put your dirty laundry inside along with some of the included detergent and fill it up with water,  

close the zipper, shake the Attack Zero bag to make sure the laundry is nice and soaked, and then gently rub the bag as you would if you were washing the laundry by hand. Finally, unscrew the small valve on the side of the bag and spill the dirty mixture out. Then add fresh water to rinse the laundry and repeat the process as many times as necessary, according to the few people who have shared their opinions about the Kao Attack Zero bag, the device is good for up to 10 rounds of laundry,

I am not sure that they are available in the UK, but it certainly seems like a good idea for people on camping holidays, and so easy to use.