This is an Alopecosa, but the species is not certain. A. cuneata is less common tha the very similar A. pulverulenta, which is abundant nationally, whereas A. cuneata is scarce and regional. However, the lattet does occur on old grassland (ie possibly Wanstead Flats) and has been found there (by David Carr, 3rd May 2017.

My supposition is just based more on its characteristics thn on close examination.