The daffodils that you get in valleys up in Yorkshire certainly spread by seed and they are also spreading down the sides of railway cuttings in Sussex so my guess would be that they do!

I can't understand,when it is recommended we deadhead,feed,and topdress them,that they come up year after year,without any help at all, on the roadside and wilder areas..so I think they must seed.Do think its because they aren't deadheaded ? I'm sure someone can inform us on here...

Certainly they spread by seeds. You can grow your own from seeds too, if you have the time and patience. They take about 7 years for the big ones to reach flowering size.
I dead head ours because I do not particularly want them to spread like that. The need to remove the seed heads to help the bulb is a bit over stated to my way of thinking.

the theory behind dead heading is that instead of the food being used to make seeds and the new blub ; all the energy goes to the bulb for next year. The plant is more likely to make new extra bulbs that are identical to the first one. seeds allow for genetic variation and the new plants may be different to the original.

Yes wild daffodils spread by seed and small bulbils. In the garden I always deadhead as they will not come true, unless you only have one variety of daffodil within the pollinators range. As OwdB says it is not necessary to remove the flowerhead but it does encourage the bulb to puts its focus into growing the flower bud for next year - knowing it has not succeeded in seeding this year. But don't cut the leaves down let them die back naturally.

takes bt 6 weeks 4 leves to die down acording to gardeners world

I have left some old flowers that were indoors on my compost and the seedheads are coming along nicely - obviously they dont take all the energy from the bulb!

no it is shared otherwise the plant wouldnt make a bulb and it would die.