longshanks,
Here is my tuppence worth going back to the original question.
The weeds in your photo's are normal run of the mill weeds that frankly any weedkiller should have easily sorted out. Bare in mind weedkiller is not residual so the weeds that re-grow are new weeds which will spring up every month if not pulled or treated.
The fact that spraying them didn't work means that you probably applied it wrongly which is what got petermeacham and ceres so worried because mis applying what you bought could be quite serious.
Here is some boring background...
Applying weedkiller incorrectly is very damaging environmentally and expensive to remove for water treatment by authorities etc which is why they are so **** hot about contractors playing by the strict rules which includes the sale of professional use products. technically you should not have been able to buy the product you did without showing them your certificates.
Unfortunately a grey area exists allowing older users land-owners of small estates etc to buy products like this hence why some sellers get away with it.
The government don't like telling people what to do in their own homes so they can't impose restrictions on homeowners for pesticides use and therefore you get lots of crazies pouring this stuff down the drain etc which i as a trained pesticides operator could be liable for prosecution if i did something similar.
This is why people get so irrate about it and rightly so. However 90% of people are totally unaware of the above and simply trying to kill a few weeds in their garden.
In your case i think the tone of peters first post was out of line but the above novel is probably why.
So In summary Peter i commend you for your vigilance but perhaps toning it down to make people aware of the issue without battering them from on top of your high horse is a better option.
Longshanks, I would try and get a refund on your 5L and get some premixed stuff with a wee pistol applicator from B+Q
Something like this which is already mixed and ready to go.
http://www.diy.com/nav/garden/garde...o-Use-Weedkiller-3000ml-9426529?skuId=9717234
You will need to pull the weeds out once dead and you will need to spray again perhaps in a month or 2 to kill any new weeds appearing