Peter is right Newbie. The most effective weedkiller is glyphosate based, and because it works by being taken up into the plant and carried around the system (hence 'systemic' weedkiller)to leaves AND roots, the more actively a plant is growing, the better the uptake, and consequently, the better the kill.
You will need to be patient and wait a few weeks for complete dieback. With the brambles and other big strong weeds you may need to be really really patient and apply two or even three times if you get any growback. But it is worth it, because it will be an end to perennial weeds. Hurrah!