The UK, along with several European countries, is planning to take joint action against Russia's 'shadow fleet' of oil tankers used to circumvent international sanctions. This initiative involves sharing information about the fleet, coordinating responses to its risks, and collaborating with the private sector to address the threat. The vessels in the 'shadow fleet' are often uninsured, poorly maintained, and violate safety and environmental standards. The plan aims to make it harder for Russia to profit from its oil resources by potentially imposing sanctions on more ships. The European countries involved seek to sign the plan at the end of the week, emphasizing the need to address the challenges posed by these rogue tankers.