This plant arrived in my well established garden last year. Probably
delivered by a bird although it is situated near a seed bird feeder.
Last year there was one stem, this year three. In the spring/early
summer there are pink flowers, at this time of year (September) it has
these deep purple/black berries. Its about 1 metre tall and wide at
the moment. Dies down in the winter.

Here is a link to a picture.
http://www.inro.freeserve.co.uk/postcards/mystery.jpg

Thanks for your help.