I had a new lawn laid approx 3 years ago and the gardener recommended Westland After cut but said not to get the 3 day type. Other than this he really recommended a lawn weedkiller but at the appropriate time when the lawn was matured.
I had a few yellow patches (my fault I think) and he recommended a good raking (to almost bare) and then lawn feed. It has been fine since.
I did also get white clover but with raking and feed it was sorted.
Being a bit tight, I used a metal colander to spread the feed to ensure good coverage. Some feed spilt and it essentially burnt a hole in the lawn so care should be taken.