Looking for something else, and I came across more info about this car. It seems to have been built by Sydney Allard for his personal use as a competition car, registered JGP473 in 1947, and is regarded as the precursor for the J2 production model. It had a different bonnet and grille , but probably sustained some accidental damage after Sydney had handed the car to his brother Leslie for him to drive, and had the front end re-modelled.
The original version of this car is on the left of this photo.