Britain is significantly stepping up efforts to tackle the dirty money funnelled by Russians and other “corrupt elites” from Nigeria, Pakistan etcetera into or through the United Kingdom, a senior police officer said on Friday.

Nigerians have been identified as among the top investors in Britain sometimes with illicit money especially by politically exposed persons.

Reuters reports that after the poisoning of former Russian spy Sergei Skripal and his daughter in March, an attack Britain has blamed on Russia, Prime Minister Theresa May promised to tackle illegal fortunes held by foreign nationals living in the United Kingdom.

“We have significantly scaled up the work that we are doing,” said Donald Toon, Director of Prosperity at Britain’s National Crime Agency (NCA). “We are absolutely looking at Russians … but we are not exclusively looking at Russians and Russian assets.”

Investors from Russia, China and the Middle East have poured billions into London, buying everything from luxury properties to entire companies, but the source of some of the wealth has been questioned by transparency campaigners.

Toon said Britain was a very attractive destination for corrupt foreign money, especially from Russia, Nigeria, Pakistan, former Soviet states and the Far East, and the NCA estimates that some 100 billion pounds of dirty money is moved through or into Britain each year.

Toon said in the next few months the NCA was expecting to expand its use of Unexplained Wealth Orders (UWOs), one means by which the assets of corrupt “politically exposed persons” or those with links to serious crime can be seized.

So far, assets worth about 25 million pounds have been frozen using UWOs. Toon admitted the process was difficult and time-consuming as each case had to be taken through the courts.

“Some people in that space absolutely have directly and immediately something to fear because they are subjects of cases we are working on,” he said.

“The fact you are not seeing big numbers at the moment does not mean we are not doing the work, because we are. You will see that come through in the courts; it will take time but you will see it. It takes time because the people who holds these assets are not stupid.”

Individuals using complex company structures to hide their links to assets were increasingly moving these from British crown dependencies and overseas territories to other jurisdictions because of their greater cooperation with the authorities.

He cited the Cayman Islands as one destination that was causing them problems.

“We are asking for information that we don’t get,” he said. “The Cayman government is entirely aware of the UK’s concern.”