I take it you tried Alfashop, Autolusso, Shop4Parts and Alfa Workshop?
There can be 3 up to 3 different sensors.
Early ones had sensors have a round housing with 2 round female pins.
Yours possibly has mid life type. Round housing with 2 male round pins.
Later cars (FL) have rectangular housings.

Which is yours?

 

Hello
I have spoken to the mechanic and he cannot confirm if a round or square fitting a sensor cable not removed as yet.
I have ordered an after market one on ebay and it shows a round fitting.
I have contacted Autolusso in London and if the after market one does not fit will have to get a secondhand one.
Thank you for the update appreciated.

 

Autolusso don't operate from London?...

You won't get a second hand sensor, I've replaced two on two different cars and after some time the sensor will weld itself into the hub so it's drilling time.

When I did one on my Alfa I removed it then went to Euro Car Parts so I knew exactly what fitted.

 

The mechanic is something of an enigma.
He says the wire is too short yet hasn't displaced the wiring and because of that said mechanic doesn't know what type of multiplug housing is on it.🤔
I didn't know the BBC trained mechanics.

 

If the only sensor that you can source is correct other than the electrical "cable" being too short, then why can't you use that sensor with some longer wires spliced between the sensor and the connector? Or altenatively, remove the existing sensor in order to find any ABS sensor that matches it (i.e. the sensor probe itself), then splice your old wire cable (including the correct conector) onto the new sensor...

Regards,
John.