The phrase "which was regulated" is grammatically correct and can be used in written English.
It is commonly used to provide information about how something was controlled, managed, or governed. Example: The price of gasoline, which was regulated by the government, has now been set at a higher rate.
He grew increasingly concerned by the prevalence of child labour in India, which was regulated only by a sparse patchwork of legislation.
The Mafia survived and outlasted Sicily's successive foreign governments because the latter were often so despotic that they alienated the island's inhabitants and made tolerable the Mafia's peculiar system of private justice, which was regulated by a complicated moral code.
Organized crime syndicates also were attracted to Nevada by the potential profits from gambling and prostitution, which was regulated to varying degrees but not prohibited from the earliest days of Nevada Territory.
Today Richards pointed out that the investigation was prompted not by Ofcom but by Sky's rivals, including cable company Virgin Media, and added that Murdoch was not as concerned about areas such as the broadband market, which was regulated by Ofcom and in which "Sky have a strong position".
Eventually the FDIC issued a ruling classifying PayPal as a money transfer service, which was regulated at the state level.
The monoterpenes of P. violacea flowers displayed a diurnal emission pattern, which was regulated by an internal oscillator in the treatment of constant light.
Similar problems are cropping up at registered investment advisers, which are regulated by the SEC and by state regulators.
The Washington regulators do not have jurisdiction over the insurance companies, which are regulated state by state.
"We're in cable television, which is regulated.
Then there's the BBC, which is regulated by a mixture of the BBC Trust and Ofcom.
Each New York State city creates its own health code, which is regulated by the Board of Health.
