Britain has imposed sanctions on 18 further Russian oil tankers and four liquefied natural gas vessels, the largest batch of sanctions to date against the country's so-called shadow fleet that the British government accuses of using illicit practices to avoid Western restrictions on Russian oil.

The 18 oil tankers will be barred from UK ports and unable to access British maritime services, bringing the total number of sanctioned Russian oil tankers to 43. The vessels included NS Bora, Atlas and Moskovsky Prospect. 

The government said it was working with maritime authorities to demand that Russian vessels with suspected dubious insurance provide details of their insurance status as they pass through the English Channel.

"Any actor that facilitates and supports Russia's malign activities could be exposing themselves to sanctions," the government said.

Russia rejects Western pressure to limit its oil exports, and in the past year, there has been growth in the number of tankers transporting cargoes that are not regulated or insured by conventional Western providers.