Once you have the judgment this can be done by having the judgment debtor attend court for an oral examination by a court officer of their financial position. Whilst not a direct method of enforcement the debtor is pressured into putting proposals for payment so it is usually very effective.
At this stage you could apply for the builder to pay money into court to abide the outcome of the case but there has to be some evidence in support of the suspicion that he cannot pay. Another way would be to get an enquiry agent to check his financial position. Most can do this so shop around. The cost is usually £300- 400.
You are unlikely to recover this cost in the proceedings but doing it could save you throwing good money after bad.
I hope this helps. If there are any further points please reply
The Q says - "for alex w"- so why are you replying?
this cannot be made a subject at cmc?