Have you counterclaimed?
Or are you just denying the debt.
You probably need to be a bit more specific regarding what it’s over, supply of goods or services subsequently defective?
It’s better to be neither defendant nor claimant, it’s better to sort it out between you.
If he gets judgement you can say you’ll pay at 50p a week and drag it out forever.
If he loses, he gets nothing, perhaps better settle for less in a negotiated settlement on the court steps so to speak.
You appear to feel you owe something, but not as much as asked in which case you could lose. Value isn’t part of the law, the law just wants to decide wether it’s been broken, i.e. a contractual agreement dishonoured.