Overpaid by my former employer over 9 months - now they’ve made a claim against me!

[Manxman]

Sometimes we are surprised at the decisions made in the county courts and one can never be sure how the opponents evidence will be viewed.
There is nothing certain in a court room....

Regarding payment of debt in the case Scottish Equitable plc v. Derby. the defence (of change of position as the defendant had paid off his mortgage) was denied
If you want to know lots more read this: https://www.bu.edu/law/journals-arch...ts/edelman.pdf

Just read that. Interesting American analysis of how England & Wales law re change of position had developed. (Although I'm horrified to see that even academic lawyers in the US use the awful phrase "... off of... " !!! Top of page 1028)

I got a law degree in 1979 and it's clear from that article that English and Welsh courts have more recently taken a more strict and more principle based approach to equitable remedies than they did back then.

Looking at the Derby decision, I have even less faith in the OP's chances of success than I did before.