Not practical to retain and rear on this one so confirmation of the ID appreciated.
No interactions present.
Creamy line along side is broken. Would be continuous in Svensson's. Only reliable in final instar which this appears to be.
Not convinced this is a final instar caterpillar, it seemed to small (admittedly hard to tell from the pictures). If I had to guess I would say penultimate instar.
Lat/Lng: 51.808, 0.1055
OS grid ref: TL452142