He says -
"Depends on what you want, if you want wild flowers etc then nothing as the grass will crowd it out, but for a traditional lawn go and ask a local supplier about a granular nitrogen fertilizer, and describe what your lawn is like now, as against what you want it to be like. Do you want it short to look nice or longer to walk on or mid length for sport etc? Is your lawn on loamy, chalky or clay soil? You want a Nitrogen, Phosphorous and Potassium formulae but the mix of each will change depending on the time of year. Don't bother with one that has weedkiller in it. Feed it and then dig up or spot kill weeds."