3L of Extra Tough Resolva Weedkiller for £1 is a great deal.
I've used this before and found it to be very effective.
Resolva Extra Tough Weed Killer.
Weed killer for control of docks, nettles, blindweed and other deep-rooted weeds.
Kills the weeds while the root breaks down naturally in the soil.
Features:
Glyphosate based weed killer
Extra tough
Ready to use
Non-drip easy lock trigger
Treats up to 120sqm (Approx.)
No residue