Hi, I think this is a plant called Leycesteria, once you have it as we did, it seeds very easily, and pops up all over the place. If left they grow to about 3 feet. I think the birds may well have sown it for you.
On balance I would be tempted to pull it out, its not the prettiest of shrubs.

Our Leycesteria (or Pheasant berry) is at around 12 to 14 feet high at the moment. (I use it to create a shady area at the back of the garden). You can chop it back every year if you want, the flowers and berries are pretty, but as Lizziebee says, it does seed easily, but just as easy to pull out. I pot up the seedlings and hand them into our local charity shop, and they sell them on.

Leycesteria Formosa sometimes called Himalayan Honeysuckle and other names too.

Quite an interesting shrub. Probably worth keeping and see what you think later as it develops.

The blackbirds seem to really like the seeds and I get lots of fun watching them trying to get to them.

I cut my leycesteria back to about 2 feet tall each spring and it regrows to about 6feet by autumn.

I think it's very attractive and the lovely flowers are followed by blackberry coloured berries which the birds love.

Lovely plant. Mine grows quite quickly. Beware though, the sap when you cut the plant can be an irritant.

it depends entirely on what space you have around it. is there enough room for it to grow into a shrub of about 6' sq with regular pruning or enormous if left to it's own devices.

Thanks everyone for the comments and suggestions. I think I'll keep it but will need to move it to a more roomy location. Do you think it will be possible to move it later in the year or is the root system susceptible to damage, maybe I would be more likely to succeed if I save some seeds and raise a new plant/plants. What do you think?
bernard

You should have no problem moving it if you get a decent rootball. Best time would be late september/early October