LONDON- Britain threatened on Tuesday to block Russian companies from raising capital in London and to expose property and company ownership if Russia invades Ukraine, saying the West must remain united on the cost to Moscow of any conflict.

Russia has massed troops and military equipment on the Ukrainian border, drawing warnings from Britain, the United States, European Union and other allies of drastic economic sanctions the moment any invasion occurs.

Last week Britain put in place new legislation enabling it to impose broader sanctions than it previously could on Russian individuals and entities determined to be involved in destabilising Ukraine or supporting the Russian government. 

This follows years when London was viewed as a particularly favourable destination for Russian oligarchs and their immense assets, with a 2020 UK parliamentary report saying that such a move had allowed illicit finance to be recycled through what has been referred to as the London "laundromat". 

Russia, which is demanding a set of security guarantees from the West, says it has no plans to invade Ukraine and on Tuesday Moscow said some military units were returning to their bases. British Prime Minister Boris Johnson told reporters the government would target Russian banks and Russian companies.

"We're...making sure that we take steps, or take even more steps, to unpeel the facade of Russian property holdings whether in this city or elsewhere..., unpeel the facade of Russian ownership of companies," he said.

"And also take steps to stop Russian companies from raising capital on London financial markets. So that is a very, very tough package."

Britain has not spelled out who would fall under the sanctions, but has pledged that there would be nowhere for Russian oligarchs to hide.

London has been a popular destination for Russian firms raising capital.

The biggest Russian IPOs were a $10.7 billion flotation by oil major Rosneft in London and Moscow in 2006. But the capital raising rush slowed after Russia's annexation of Crimea from Ukraine in 2014. Instead, companies have by and large switched to the Moscow exchange.

Last year retailer Fix Price held a dual listing in London and Moscow, raising $2 billion - the biggest IPO since Western sanctions were imposed in 2014 - and another Russian firm, London headquartered IT group Softline, listed in late 2021.

The London Stock Exchange carries 24 listings of depositary receipts from firms incorporated in Russia - meaning they can be traded from London - including lenders Sberbank and VTB, energy giant Gazprom and oil firm Lukoil.

(Reporting by Kylie MacLellan, William James and Sujata Rao-Covereley; Editing by Kate Holton and Mark Heinrich) ((william.james@thomsonreuters.com; +44 207 542 3374; Reuters Messaging: william.james.thomsonreuters.com@reuters.net))