Bloodhound originally used a Cosworth Formula 1 engine as a fuel pump but with the new sponsorship from Jaguar Land Rover, a 550hp Jaguar engine has been pressed into service.
I may be wrong, but I had heard the reason they are not using a Cosworth F1 engine is because there are no Cosworth F1 engines anymore. They are no longer being produced, due to the change in engine regulations.