Trying to identify several weeds

Looks to me like Fallopia baldschuanica, aka Russian vine or mile a minute plant (syn. Polygonum baldschuanicum). Cut it back, dig out as much of the root system as possible (easier said than done) and don't try to compost it (it will regrow). Then treat any regrowth with Roundup. It has the potential to be highly invasive.

Are you located in Australia or NZ? A strong possibility is that this is rambling dock or potato vine as described in this wikipedia article. The arrow shaped leaves and red stems give it away. If not this one and you are located elsewhere, it would be helpful if you indicate where.

Edit: an alternate suggestion is Polygonum sagittata which fits the description fairly closely; however this species is not mentioned as being found in the UK either.