Looks more like a Willow Warbler to me but is is a bit green for this early in the season. Did you hear its song? That would identify it.
Songs are:
Willow warbler: musical cascade down scale
Wood warbler: repeated single notes on one pitch accellerating into a dry trill
Chiffchaff: chif chaff
I think it could be more likely a Chiffchaff, as I 'think' the Willow Warblers would have a more yellowy appearance around that time (last month right?).
dfrear ~ I'm intrigued to know how you came up with juvenile Blue tit :shrug:
Thats Steve, i'd recognise him anywhere
Ok i trust you Donna honestRay, if you were to hear one you would recognise the song from the description - Trust me on this one.
Take a look at http://www.bto.org.uk/birdfacts/indexa_short.htm
There are bird song recordings against most species that will help.
This is another decent bird ID site
http://www.rspb.org.uk/wildlife/birdguide/name/a/index.asp
Frankly this specimen could be either CC or WW... :shrug: ... there are not enough clues from those two images to make even a reasonable stab either way... ... and without hearing the song this one will have to go into the either/or folder imhgo...