lily beetle

I have found what looks like a lily beetle on my potatoes. Does anyone know if lily beetles are usually a problem on potatoes or is it likely to be something else?

I would guess at Soldier beetle. The commonest of these is the Hogweed Bonking beetle. They are predators of other insects so are to be encouraged.
http://www.gardensafari.net/english/soldier_beetles.htm

There is also a sailor beetle with blue/black wing cases.