Bird watching

I'm spending too much time gazing at the birds in the garden, mainly due to having to sit down and get relief from sciatic pain.  I'm unsure what this bird is although I've looked up the RSPB site. I'm sure this is a male and female of whatever it is. Due to the bright green colour, E thought it was a budgerigar, but I know it's not.  it has been a constant visitor to the feeders for a some weeks now.