It is the Buxton Memorial Fountain and you can find it in Victoria Tower Gardens, just south of the Houses of Parliament wedged between Millbank and the river.
Apparently it was originally constructed in Parliament Square but moved in the 1940s and placed in its present position in 1957. It was commissioned by Charles Buxton MP to commemorate the emancipation of slaves in 1834, dedicated to his father Thomas Fowell Buxton, and designed by Gothic architect Samuel Sanders Teulon (1812–1873) in 1865.
It surely has to go down as one of London's more outré and colourful adornments. Not only does it have that "spire" of coloured encaustic(?) tiles, but it is carved with various animals including some very dragon-like iguanas/lizards.
Not the best of photos as it was taken on a horridly grey and, as can be seen by the puddles, rather wet Sunday morning.