In Australia, we had washing machines that washed the clothes in cold water, and we bought special powder for this purpose. Is anything like this available in UK? I know you can get cold-fill machines, but they heat the water up, so they are no good.
Yes, cold wash machines are available in the UK. See here for one example..
But it should be noted that cold wash detergents do have a certain minimum temperature requirement below which they don't work very effectively. With mains water temperatures in the UK in winter, it might be necessary to first half-fill a cold-water-wash machine with warm water so as to obtain an effective wash when using these detergents.