I try to use a John Innes no 1 for seeds as it is low in nutrients and doesn't get too wet.
if I haven't any to hand but I always use fresh in case there are any diseases in the used compost that will affect the seed/seedlings.

I think starting seeds in used compost is best. Seeds are usually packaged with their own food supply that has everything they need to get them off to a good start. Growers usually opt for a soiless mix and fresh compost has plenty of pathogens and can be too harsh on new seedlings. Once they grow their 2nd set of true leaves, then you can transplant them into the richer compost.

Fresh compost that you buy is meant to be sterile [ie pathogen free] and weed seed free, though I don't tend to find that it is totally free of weed seed .

Do you plan to buy compost or use your own home made compost?

As Bathgate says most seeds have their own food supply and their first leaves [cotyledons] rapidly start making food for the seedling. Nutrient rich compost is therefore not necessary and as you water it they will wash out and be a waste.

In the UK growers use soilless compost to keep the mass down in order to reduce transport costs.

If you think about it in nature seed lands on soil and grows away happily in their native conditions.

Thankyou both.I bought a sieve but it lets all sorts of bits of stick through. I didn't have any of my garden compost, which is much more free of bits of wood.I used fresh compost but I'm going to get some seed compost for next time. My used stuff is the same texture as the fresh.

I get it off the milkman as I don't drive a car and it is so convenient and is ok I think, but not for seeds.

I love plants that self-seed SBG and wild flowers are good at that ( a bit too good really). I have more and more native plants and they take quite a bit of control. Three cornered leek is very prolific so I don't allow it to reproduce, The flowers are pretty and I have jars of them around the house at the moment; they last for ages in water. It feels a bit cruel though.

I too have lots of self seeders but some are always welcome as family favourites, Nigella being one of them.