Like 'hammerman' I use Verdone, but I use Verdone Extra Lawn Weedkiller. It's a spot treatment spray which claims that one treatment gives season-long control of weeds. I used it last weekend; the weeds have shrivelled up, but the grass is fine.
If you have a relatively new lawn, check the labelling to make sure the weedkiller is suitable. A lot of products are for use on lawns over six months old, however the Verdone I use is OK for lawns over two months old.