Weed killer suggestions!

Good Afternoon,

I'm getting married this weekend coming up and we're having a BBQ to celebrate. So trying to get the garden all clear. I bought some resolva weed killer(cost about £42) and it's done absolutely nothing! All weeds are exactly how they were and I absolutely soaked them with the stuff, roots and leaves! My garden is completely tiled but the grout has come up in quite alot of places and weeds have grown out the gaps...

What can I use that will kill them off effectively?