I have to say getting the correct compost is really not easy. I used to swear by our DIY B&Q the biggest bags and when I saw Which? confirm its best buy status, I was very pleased. But no, after they won the accolade, the quality has gone down hill. Twigs and mould and bugs all grew around, over, next to the seeds and in the end, the seedlings died. I had to complain and was told it was government directive that the compost must be enhanced ie. with waste materials (include human excrement


) added in! So now, when I see the word ENRICHED, I know what it means .. I have bought MiracleGro enriched and it has dried up very quickly... So I am none the wiser. But I will follow
@johnny canoe 's advice - use old compost, but sterilise it and add fertiliser a bit later or chuck in slow release granules .. Nothing wrong with using used compost if you sterlise it and fertiliser it.