This unique picture strongly appears to have been made in Germany instead of the UK. The steam turbine exhausts a thick jet of steam from under the rear fuselage, and some steam is coming from the rocket's exhaust. A pilot with goggles is sitting in the cockpit. In front of the main wheels there are small blocks of wood, that the Komet would jump when sufficient thrust was generated (note that they are not the '6MU' wheel chocks seen in the Hyde Park photos). It looks like it is ready to take off. The photo has been subjected to some retouching to enhance the aircraft's outline. It also appears to lack the dark band of paint (or tape?) on the fin cap that is visible in the Hyde Park photos.
Source: 'Ein Dreieck fliegt; die Entwicklung der Delta-Flugzeuge bis 1945' by A. Lippisch and F. Trenkle