The above link credits the Albion Band's Battle of the Field as the first recording of 'New St George'. It did, however, appear initially on Richard Thompson's debut solo recording Henry the Human Fly, as fogie says. This also had 'Nobody's Wedding', which I thought a truly great song but which RT now dismisses as 'silly'.

I still have the album on rapidly disintegrating audio tape. The opening line of 'New St George' differs slightly in that RT sings 'The time has come for action....'   The song's ecological message was way ahead of its time.