Thanks everyone for your replies. I do hope it isn't slug eggs - have had enough of the blighters this year!
I don't think it's water retaining granules but it did appear after I planted some bulbs. The soil isn't especially compacted. Could it be some type of mould or fungi? I do live in Lancashire, a wet part of England!
I've discovered some patches of a slimy jelly like substance in a flower bed. Has anyone got any idea as to what this?