Warbler

I'm guessing that this is probably a Marsh Warbler, rather than a Reed Warbler.  The legs appear to be paler that the Reed Warblers and the birds underside has a slight tinge of yellow to it.  

As you can see, it has managed to catch a flying insect of some sort and when I took this picture it was about to fly back into the reeds to feed it to its fledgling.