You can by one of the 'weed and feed' for your lawn in any garden centre, which is usually applied in spring and again 6 weeks later, You do need to follow the pack instructions. There is still time for one application this summer. Also if you mow every 5-7 days in the growing season that weakens the weeds. If you had had the odd Dandylion there is also a spot weed killer for lawns, you can just spray the individual weed.

I also had a problem with dandylions in my lawn...I just kept pulling them out....a backaching job....but in the end I won. I will not use weedkiller in my garden....not too good for the insects...and we don´t have enough of those nowdays.

Like Rogi, I find the only permanent way to get rid of them is to dig 'em out - you'll win in the end!