Have you checked the fusebox on the drivers kneecap?
Wiring diagrams show fuse 12 and 15 (12 powers the ecu and the blower motor so I guess its fine, 15 powers the PWM box and MAX DEF switches/other stuff so I guess it is fine too).
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Red wire comes from fusebox (4) to the blowermotor (+), black leaves the motor to the PWM box (255), Grey wire should be power ground for the PWM box and ends up on chassis ground (222, changes color to black as other groundwires are added to the mix).
You can probe the the wires with multimeter, motor should be getting constant 12V from the fusebox, black wire from motor should also be 12V when the motor is off. Grey wire should be always gounded.
When blower should be on full, the black wire should be near 0V, when it is running but not on full blast, it might be anything depending on how good your multimeter is reading the signal (best case scenarios is that it has duty cycle function).
"It was working fine but would cut out momentarily then come back on. No matter what speed you put it on there is nothing."
So it used to oscillate but is now completely dead?
Sounds like bad ground to me, measure the grey wire when the fan switch is on full.
Use chassis ground when measuring, not cig lighter or anything that has wire running to groundpoint.
UK car so the groundpoint connections might be mirrored, sometimes not so check both sides.
