That is Japanese Knotweed, a ferocious and notifiable thug which needs to be eradicated before it takes over every space available to it. Council eradication teams use Glyphosate, but with lockdown I doubt they'll be doing very much. I've even seen it pushing up through tarmac!
Don't break it off at the base as it will simply grow new stems, more than it had before. Dig down and get as much of the root out as you can, and pray it doesn't return or hasn't spread. Sorry to be the bearer of bad news! The plant was brought over to this country by Victorian plant hunters who thought its colourful leaves and heads of shimmering white flowers would make good focal points in Victorian gardens.

Sorry to disagree but it isn't JK. The leaf shape and positioning is wrong for JK so relax on that point.
as to what it is that's another thing.
it looks as if it is shrubby/woody. I was thinking along the lines of willow/cherry self sown seedlings.

did it just appear or did you buy it and lose the label?

I was going by the colour of the stem and growing tip SG. It's mostly been eradicated down here so I haven't seen any for a while. This old memory ain't what it used to be.:) Apologies if I've been prematurely alarmist.

This just appeared. There are three shoots of various sizes.

Judging by the opposite leaves (two at a time) I'm thinking privet or lilac suckers, maybe even a viburnum or honeysuckle. knotweed, cherry, and willow all have alternate leaves (one at a time). Some idea of the size of the leaves might also be helpful. When identifying plants, details are very important.

Thanks for all your suggestions. There is a very old lilac tree about two foot away, although the leaves look a little different (old one has smooth leaves, leaves on shoots are a bit `wrinkly) so it is probably what it is. Again many thanks for reading and relying

That will be the Lilac then! These are the original plant, your's is probably grafted. I have loads of these come up around the base of an old plant, annoying to have to cut them all off, but they will take over.