Could this be a Wood Warbler or Chiffchaff.

Hi Mr R

Definitely both Chiffchaffs. At the very olive end of the scale but dark greeny plumage, dark bill and legs, dusky underparts, short supercillium and wings and quite prominent eye ring all point to Chiffchaff. Wood Warbler would not only be in Africa by now but would be bigger with longer wings, much brighter green above with lemon yellow throat, silky white underparts (including the vent), a long supercillium and pale legs....

We usually have a Chiffie or two wintering in our reedbeds

Hope this helps somewhat

H ;o)