Bird ID

Hi there - I was hoping I could get some help identifying the attached bird.  I took it whilst having breakfast before heading to work.  I'm located down in Sussex on the south coast.  It's about the size of a goldfinch, behaved a lot like one as well, but is yellow/greenish in the chest, and the rear feathers looks almost sparrow like in colour and appearance, it had black facial markings as well (it sat for a while eating sunflower hearts until a pigeon frightened it off) - unfortunately the camera is on maximum zoom, so the images arent good.  Many thanks for any help you can offer!