During the Bridgend raid, a businessman, 58, was arrested on suspicion of money laundering.
Cash is suspected of being generated from overseas organised crime.
A City of London Police investigation was launched in March after it received intelligence a UK bank account was being used.
Police believe that cash was generated through overseas organised crime - including Ponzi schemes - and on foreign exchange markets, before it was laundered through the man's company bank account.
The business is listed as being involved in test drilling and boring with an annual turnover of £250,000.
But in November 2015, £13.2m ($19m) was transferred into its account, converted to Euros, with most sent on to Georgia.
Then in February 2016, a further £29.1m (€37m) was transferred into the account, with the arrested man claiming it was for the purchase of a Sri Lankan tea company.
In a statement, City of London Police said it believed the £30m of bankers' drafts was the "the biggest ever money seizure made by UK law enforcement".
"We believe this man's business account was being used by a global network of organised crime operators to launder tens of millions of pounds of stolen funds through the UK and then out into bank accounts around the world," said Det Insp Craig Mullish, from the City of London Police's money laundering unit.
Bankers' drafts worth £30m have been found in what is believed to be the biggest ever money seizure made by UK police.