Looks like a poppy type plant to me..not sure though..:)
Hope someone will identify it for you soon.

My first reaction was Poppy , same as Michaella but also not 100% certain

Don't think it is a poppy, are the leaves rough and or hairy?

On the other question you said it is growing very quickly. Though I'm not sure, that makes me wonder about Heracleum mantegazzianum, giant hogweed.

I don't think it is but, because it looks quite like some of my pictures of young plants, I'd suggest you treat it with great suspicion until you get a confirmed ID.

Oriental poppy was my first thoughts

My first thought was some kind of poppy, but the second thought was a relative of the harts tongue fern. What is the back of the leaf like?
Compare it to Asplenium scolopendrium 'Cristatum' Crested hart's Tongue Fern http://tinyurl.com/c7xzhqm
or Phyllitus scolopendrium undulatum 'Crispum'
and see what you think.

What is the pole that shows in the top left of the photo? Could this be a bird feeder? In which case it may be some sort of seed from the feeder that has sprouted!

I don't know...but I'd like to. The leaf shape is very similar to the acanthus (variety unknown) which is common here - but the colour is all wrong...

I've been pulling loads of these out - the only good thing about all this rain is that they come out easily!

Good point Volunteer

Does look like acanthus to me but not 100%

Thanks everyone will check out your suggestion