No - it is a beetle; a scarab or relative.
There are a lot of species...
The family used to include the well-known May bugs and June bugs (chafers), but they have recently been moved into a family of their own.
Ah great thank you so much, and such a prompt reply! Should I expect to see any more of them in my house or do they tend to be relatively lonely, and if I let it go outside is it likely to come back in again?
In the UK, some of the scarabs occur in fairly large numbers (thinking cockchafers).
With this one, though I'm not sure which it is, I suspect you'd see only a few. Yes, it might come back in if you let it go, but that's the best plan, IMO.
If it is showing a tendency to be attracted to light, the thing to do is: turn the outside light(s) on, turn the inside lights off, open the door/window, then put it out.