Photo a bit out of focus but if its a money(jade) plant it might be mealy bug infection. I have just cleared (I hope) my jade plant of this.

Hi Charnwood, what plant is it?
if its fluffy clusters then either mealy bug or woolly aphid. if its an overall white powder then possibly one of the mildew plants.

It could be mealy bugs. They like warm dry conditions. To get rid of it dab it with a little brush dipped in meths.

Looks like a mildew. I'd snip off all the infected bits & remove the top inch or so of soil- bag & dispose. Then put the plant in a nice dry, bright spot. Beware of it carrying to other indoor plants! Water very lightly from the bottom.
There are various sprays you could use including DIY milk mixes, sodium bicarbonate & mildish hydrogen peroxide.
These types of mould are everywhere outdoors but bringing the plant in gave the mildew better conditions in which to thrive

If you're keeping it indoors because its cold, that suggests its something you'd otherwise have outdoors and not a houseplant - Its not possible to tell what plant it is from the image, nor are the white deposits in focus... can you post a clearer photo and tell us which plant it is?

Thanks to you all its an Aeonium, the white stuff is tucked up under some of the leaves, I had a fabulous huge one but the frost got it and I'm now starting again and hoping not to lose it.

Hmm, doesn't look anything like Aeonium, well, from the bit we can see in the picture... as Seaburngirl says, likely mealybug or woolly aphids... without another photo that's in focus so we can see the white areas clearly, that's the best guess.

Another pic properly in focus would make it more likely it could be identified accurately, if you can manage it.