500-1 chance.

I came up from Brighton to London Victoria at about 2pm.  From there we went to Beddington sewage farm.  Apparently 500+ young Tree Sparrows fledge there every year, so I should have a good chance to see one.  Unluckily you are not allowed to go inside the reserve without a key.  But you could get an okay view from outside through the fence.

On the landfill site there were hundreds of gulls.  Around the lake were: Teals, Herons, Lapwing, Coot, Tufted duck and Black-headed Gull. Along the paths were Chiffchaff, long-tailed Tit, Blue and Great Tits, Robins, Magpies, Jays, Carrion Crows, Jackdaws, Sparrowhawks, and a Peregrine Falcon!  And the number of Tree Sparrows I saw was a big fat zero!  500-1 chance of seeing one, but no luck.

Despite the lack of Tree Sparrows it was an enjoyable walk.