These are the birds that I feel could be possible, and that I have not seen in London this year, and in most cases, ever. The LNHS recording area is a circle of 20 miles radius, centred on St Paul's Cathedral. Very approximately, this is the area enclosed by the M25, but a proper map can be found here.
I'm reasonably well plugged-in to the London grapevine, but no-one can know everything, so I would very much appreciate any news you may have on any of the below. Obviously some are less likely than others, but if you have one (or more) on your patch, or in your garden, I would like to know about it!
Great White Egret
Great Grey Shrike
Willow TitCommon redpoll