Is this a weed.... HELP!!!!
 

Hello!!!
I need your help people!!
At first glance, this plant appears somewhat like a clematis, grows like wildfire, quite slim, pink coloured stems with feeder shoots coming off it,that cling, green glossy leaves, and the tips look similar to small clematis buds, although these never flower.
The nearest picture I've found online, is Japanese Knotweed but not 100% sure it's this, it grows up from the ground next to my house starting from March & goes mad. Trouble is, it mingles in with the plants I have growing in a pot next to it which have 2 clematis in.
Any help greatly appreciated.
Claire xx