Nearly got to work and stopped when I heard a strange rattling sound. Checked bike over - one of the nuts on the mudguard stays had worked loose.
Now a dilemma - I had a set of allen keys, but no spanners, what to do?
Then i remembered that I had wrapped some Duct tape around a 5mm allen key (top tip Grahame) and wrapped it around the offending stay - sorted.
Moral of the story - Duct tape, don't leave home without it