UK Car Repair: A 6 month repair, legal recourse, aa road

Question
6 months ago my mechanic, took his loaner car back after declaring that my car would be okay to continue on its 70 mile round trip with the oil pump light on.

34.65 miles into the journey, the car disagreed with the mechanic, so after investing 160 quid in the AA road service our car went back to the aforementioned mechanic - the devil you know... After all he returned our loaner car after the damage had been done.

So 6 months later after our valiant mechanic working with the warranty company, we have been presented with the option of buying the just better than nothing loaner or buying a 2000 quid refurbished (probably dodgy engine).

Technically – as a layman I can determine – it’s broke; do I have any legal recourse? As I have been financially challenged through this period.

Answer
Engine should never be driven with the oil light on.
any mechanic that tells you otherwise is dangerously irresponsible.

it' a direct result of his advice that your engine disintegrated.
He's legally responsible for the damage in that respect.