Bird ID

[shivvy]

I have noticed a little green bird in my garden and am having probs identifing it. It looks like a greenfinch but smaller and more uniformly green. He was pecking flies off the front of the parked car.
Someone has said that it might be a chiffchaff or a willow warbler but when I look up their pictures they don't seem green enough (in fact the chiffchaff doesn't look green at all?!)
Any suggestions?

[Thunderbird+]

Could it be a juvenile Goldcrest ? It's greenish in colour but lacks the crest,