Your new lawn has had a tough first year, I am sure it would appreciate a little TLC now. Look for Spring Lawn treatments, Wilkinsons have boxes of it on their shelves at the moment, as will lots of other places selling gardening stuff. Follow the instructions on the box and you can't go far wrong.

I'd let the lawn get into growth before feeding touch. It won't take long, hopefully!

Hi,
I'd also give you a good warning, be very very careful how much lawn feed you use,
Ive seen so many lawns turn black "inspite of instructions being followed,

Let the lawn start to really get going before you start feeding it,
Dec isn't the ideal time to be having turf laid in
certain parts of the uk, and the prep pre laying again is important,
Instead of long warm evenings december offers long very cold evenings and little if any sun, followed by months of even colder days and nights,
It want take long for any plant to die and turf is a plant.
As ive said let it settle, yellow patches are not a good sign,

But let us know what you do and the results.

My lawn is quite new as well and is on compacted clayish soil. I fed it general weed and feed at the beginning of March and did another at the weekend, both after a good raking. Looking much more green now and the yellow patches are greening out.

A spring feed is best as it is higher in nitrogen than autumn feed.

If the lawn is established then leaving it to green itself as Worthy has said is a good option as well. I would still be raking/scarifying the yellow patches out to stop compaction and to allow growth.

Thanks so much all for your advice.. I think I will try find a Spring feed, but I hope to find a product that does just feed and does not kill weeds, as I am worried about the black patches Dungy describes. Thanks all for your advice, will try to remember and do b4 and after pics!