I feel it has to be the Mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae) - but it sure is a small one. The larvae of these beetles will often feed on pieces of bread brought back by birds into loft spaces or dropped down chimneys. They can also feed on starchy food debris beneath kitchen cupboards and appliances. They are not really a pest, just taking the opportunity to clean up for us, and they will not cause any damage to furniture or furnishings.
Just chuck any you find out the back door.
Thanks so much for the replies, we have been a bit worried as we just bought the flat as first time buyers. I think it looks most like the Mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae). We have had bigger ones than that. We have all of a sudden (in the last few days) found quite a few of them like 5 a day or so. Do you know the reason for this? They all seem to be in our bedrooms rather than the kitchen. We live in an old house in a top floor flat - clould they be on the roof? we have lots of pigeons flapping around too so it could be them.
This is another one we fund today that was much bigger!
This new photo confirms bombuslucorum's ID: Mealworm Beetle. The natural habitat for their larvae are bird nests, so I guess you are right about those pigeons, they are the ones who 'invited' the beetles in your home. But don't worry about them. They are harmless to humans. In fact, mealworms (their larvae) are a delicious food supplement with an almond-like flavour.