What do you do with the foliage most years, Masterloucat? And do you feed them? Daffodils should be fed while they're in leaf, just as the flowers fade, for six weeks, and the leaves left intact for that time, watering if necessary. After six weeks, you can cut the leaves off. If you've done anything different from this before, feed them this year while the leaves are present, and let the leaves die back naturally - with any luck, you should have flowers next year.

Too much shade will often prevent flowering, too. In my experience, they need at least 4 hours of direct sunlight a day, while they are in leaf, to produce blooms.

If I have a clump of daffs that don't flower one year, out comes the fork whilst they're in the green and I dig them up and split them. spreading them further around, they always flower the following year.
But then again someone else might say I'm worng again.

I won't say you're wrong! That works if they are overcrowded, but not if there are other problems. Of course, none of these sources of trouble are mutually exclusive! : )