Without question, the most exciting and tense moment of the build so far.
Nervous of potential leaks, another final round of checks was performed on all the plumbing fixings. Then the engine fluids (6L of diluted coolant; 7L of oil between the Engine and Dry Sump Tank; 30L of fuel) were added - the coolant is filled through the Expansion Tank and takes some time to percolate around the system so requires regular topping up. A final check for leaks and drips was made without incident.
The recommended pattern of first engine start was followed:
Disconnect the Inertia Switch (on the rear of the bulkhead) to prevent the Fuel Pump from operating.
Switch on the Ignition Switch and press the Start Button - monitor the Oil Pressure gauge to look for increasing pressure.
When Oil Pressure is seen, reconnect the Inertia Switch.
Switch on the Ignition Switch and deactivate the Engine Immobiliser - listen for the Fuel Pump - Switch Ignition Switch off.
Repeat step 4 until there is a change in the tone of the Fuel Pump indicating the fuel line is primed.
Reconnect the Inertia Switch and then start the engine normally.
Following the above process, I found that there was no oil pressure until the third or fourth turnover of the engine, when it suddenly rose to around 2.5 bar. It then took a moment to realise that the Immobiliser need to be deactivated for the Fuel Pump to operate in step 4 and, with the benefit of hindsight, I should have run the Fuel Pump a couple more times to make sure the lines were fully primed. The change in tone from the fuel pump can be heard clearly in the video below when the ignition was switched on again just before the first successful turnover.
After that - the engine fired up successfully on the third turnover. It required some manual intervention on the throttle cable to keep it from stalling until the engine warmed up, but otherwise everything went very smoothly.