It's Anthrenus verbasci. They are quite common at the moment, I've killed several in my house in the past fortnight. The larvae infest things like furs and woollen clothes. And, unfortunately, insect collections, which is why I have to be vigilant.
I would imagine that every house in the country has one or two, so I wouldn't worry. If I found ten I would worry. I routinely destroy them because I have to protect my insect collection, which they can damage extensively. If you have valuable or antique clothing, then it might be worth checking it over just to be sure. They won't attack man-made fibres, they mainly go for wool. I once had a load come out of a sheepskin rug.
The life cycle, as I understand it (someone here may know this better than me) is that after pairing, the females will lay eggs in wool. These will turn into small larvae abut 6mm long with a rather hairy-spiky appearance. These will munch on your clothes, wool carpets, or whatever. Then they will pupate, at this point you might find them wandering round the house looking for a quiet spot. The adult beetles then emerge the next spring - they may have more than one generation a year, I'm not sure. They are attracted to light so they usually end up on your windowsills.