The 623E number plate on the car was a Staffordshire trade plate. In the UK a trade plate is a temporary number plate used by vehicle manufacturers, motor traders or vehicle testers to save them the cost and time to register and tax every vehicle temporarily in their possession.
On Tuesday 3rd November 1953, Sir John Black asked Ken Richardson (Competition Manager at Standard-Triumph) to take him for a trial run in the new Doretti and give his opinion. Unfortuately as they drove down Banner Lane, Coventry, a works pick-up truck turned across their path to enter the factory gates. There was no hope of stopping and Sir John Black and Ken Richardson were badly hurt in the resulting accident and the car was a complete write-off. The only redeeming feature of this accident is that in a car less strongly built they may have been killed. Very shortly after this, Sir John retired from Standard-Triumph.
... Information from The Authentic Doretti Story by Frank Rainbow