Well Euan, serious investigation is required. At the front of the engine you could be looking at the thermostat tower and water pump or the hoses to the radiator, if you’re lucky. Thermostat tower and water pump are known to fail.
The worst will be the valley pipes though they don’t normally leak from the front.
Find yourself a reputable Jaguar Indy and get it pressure tested, this will be the cheapest way of identifying the fault.