As per David's last post plus some checks below:
Bridging the 2 big terminals on the starter motor only engages the starter to spin and may not engage the starter pinion gear into the flywheel ring gear. Pull the small spade terminal off the solenoid and bridge between the big outer terminal and the spade terminal on the solenoid to test the starter, battery and connections (with a health battery).
Check the inertia switch is not tripped (on the left hand side corner of the engine bay, press the rubber switch cover to reset)
Check fuse No. 1 in the under bonnet fuse box (this is the power feed to the starter relay + the engine ECU)
Check fuse No. 20 in the fuse box in the driver’s footwell (this is the cranking signal from the ignition switch to the starter relay)
I the fuses are OK pull out the starter relay (it’s behind the boot carpet on the left hand side)
With the starter relay removed and using a short piece of wire as a link, bridge the connections on the relay base between the white with a red tracer and the brown with a red tracer wires, then try to crank the engine on the key.
This bypasses the starter inhibit on the alarm BCU.
Let us know how you get on.
Brian.
And welcome to The-T-Bar