Ok, taking the lid off the fermentation bucket seems to have helped! Since
replacing it it's perked up and is now pliping once every 16 seconds or so.
I think it was an issue of not enough oxygen for the yeast (I did put the
airlock on early according to the recipe I put it on after a few days
whereas it suggested to "cover and leave for a week" or somesuch).

Thanks again
Ceri )