Feeding them, as per this link, might help:
http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=658
(See also the advice about lifting and replanting overcrowded bulbs; that suggests that bulbs which have failed to flower one year might still be persuaded to do so in future years).
Many of my daffodils have come up blind or not at all these past two years. I've never been able to get blind ones to reflower, I'd buy some new ones Mags.
I had a lovely sweep of snowdrops and very few of those appeared this year too.
Thanks for your suggestions all of you, I think I will just lift them and buy new later - snowdrops and crocuses have done well, so have had colour anyway