If the company is based in the UK you could have had a local representative to file a claim. It may be of course that you have no legal recompense; however I'd

If the company is based in the UK you could have had a local representative to file a claim. It may be of course that you have no legal recompense; however I'd exhaust all possibilities in that direction before sabotaging a site. Perhaps what's needed is a "name and shame" list of deadbeat clients somewhere that developers can check before accepting work.