Below sentence is copied from The Economist.
Firms operating there will be subject to rules based on English common law, enforced by independent courts, the government promises.
I'm not able to understand the sentence structure and the usage of commas in the above sentence. The first part of the sentence (Firms operating there will be subject to rules based on English common law) looks me a complete sentence (independent clause), but the second part (enforced by independent courts, the government promises) is using enforced..... as a verb or as a noun?. How is the writer using commas to split the ideas?
Please explain the structure of the sentence.