Apply glycophosphate to it. The only way you have a chance of ridding yourself of this is to kill the root system. If it appears again on the lawn or garden border apply glycophosphate but you will have to accept some collateral damage from this treatment on the grass and other plants nearby.

If it were to be Japanese knotweed then don't panic, at least your on the ball with it and it it can be dealt with swiftly, here's what I have done to eradicate it in the past, I had a large area to deal with on the allotment which had completely taken over someone else's plot, I found that cutting the canes down to about six inches in late summer then trickled in to each cane some glyphosate which as the plant was dieing back meant it took the glphosphate right down into the root system, this worked well with only a small amount coming back the following year and once weed killed again the problem was solved and no more knotweed.

I'm not convinced this is Jap kw. the stems have a bamboo like appearance where as this doesn't.
have a look at the rhs site about it and see if it is a match.

having said that I don't know what it is though.

My son did this to his and said it worked well for him too. There will be no need to dig it up if you use this method carefully. But I would do it as soon as the canes are big enough to have hollow stems - you can always do it again in the autumn if its still there. My thinking would be that if you leave small amounts all summer they will have time to spread further?

I agree with SBG, don't think this is Japanese knotweed

It might be Japanese knotweed - long established plants tend to produce a thicker cane like structure from the ground as an initial shoot, but its hard to be sure what this is until some leaves have opened up properly. I'd be inclined to let some leaves open and decide its ID for sure, or you'll be panicking every time something like this pops up out of nowhere. Post another pic in a few days as it advances if you're still not sure, it should grow rapidly if it is knotweed.

It does seem odd its appeared out of nowhere - where did the compost you bought come from, was it a commercial, bagged potting or soil conditioning compost, or something else from somewhere else? And how long ago did you use it in the garden - I'm confused as to why it should be growing in a stoned area, because presumably, you've not used any compost in that area. How long have you been in the same property and doing gardening?

This looks exactly like my tuberous begonias that are beginning to sprout up again now that spring is breaking. It has the exact form and color. I never had knot weed but I agree with Seaburngirl who is extremely smart and knowledgeable about such things. KW seems to be more woody while these are soft and fleshy - as begonias are.

it reminds me of a shrubby paeony. was there one in this area?

Strangely enough, SBG that's just what I've been looking at since the red stem emerging. Himalayan balsam,
Impatiens glandulifera was another thought. But as already said, there are many perennials with red stems that it could be, so by letting it grow taller and then cutting the stem and dripping glyphosate into the stem should sort it out.

Himalayan balsam is an annual and it produces very obvious cotyledons and isn't usually multi stemmed. but time will tell.

Hi guys that's brilliant that so many of you have replied. Thanks for all the advice. I will leave it a little longer and see how the leaf develops to see if I can definitely identify it. I have some bayer stump killer which kills knotweed I will apply it neat once I know more.
Many thanks chris

let us know what it turns out to be. add a photo too so we know for sure please.