Warbler? South West, UK. (1 Viewer)

2 of these darling little birds visited our garden 2 days ago - 24 March 2013, in a bush and also flitting around in the grass.
They are very small - much smaller than a Robin. ...and also extremely 'agitated' in behaviour, only staying still in one spot for a fraction of a second (hence very difficult to try and photograph).
The head and body appeared almost as 'chubby' as a long tailed tit.
It was a very overcast day, so the colours on the photos may not be correct.

I wondered if there were Yellow-Browed Warblers, but have to admit I had never seen any before, or even heard of that type!

Looks like a Chiffchaff. Did either sing?

They are Chiffchaffs

Sadly they both worked away very quietly. I am very familiar with the Chiffchaff call, but have never seen one close up.
Thanks to all for ID'ing it for me.
PS. It doesn't look like any of the Chiffchaff pictures in the books I have, it looked far 'chubbier', but then it was very cold.