Guessing unknown projection of Webapp

I have a series of points around the greater london area (may be also around 100-200kms away from it) like those here in the format Lon, Lat:

43032.1,32681
95816.5,34473.8
15439.3,-13987

The Application to which those points are transferred uses leaflet but does not use any of EPSG3857, EPSG4326, EPSG3395 from http://ift.tt/RFBUUp unfortunately. At least that's what I found out when using the proj cmdline tool like this:

echo -48884.4 64535.7 | cs2cs -f "%.10f" +init=epsg:3395 +to +init=epsg:4326

I really tried a lot of possible projections and flipped the order but I cannot find a way to get a plausible result which should be something like 51.xxxx -0.1xxxxx

Does someone have any idea on what projection may be used here?