Is it tall - I can't quite tell. If so, it could be Oenethera (Evening Primrose). It grows taller and taller with more yellow flowers opening as it grows. It has a lovely fragrance in the evening, because it's pollinated by moths.
It is an annual and seeds readily.

I also think that it is Evening Primrose.

Certainly looks like mine do.

Great. Thanks, its actually in the wrong place now.

Sorry, Nics - you may have my attention, but I'm afraid I can't answer your questions! :-) I assume you don't mean the purple flower, which I think is Lychnis (rose campion). If the plant you mean is thorny like a rose, with similar leaves, it might be a rose seedling, which probably won't flower, but just grow a bit like a bramble.
I haven't ever grown acers, I'm afraid, but I'm sure someone else will be able to offer advice.

Other people have asked this acer question and the answers seemed to be that it was probably due to the strange weather.