LONDON, July 15 (Reuters) - The British government's stake in NatWest fell below 20% on Monday, the bank said, moving the lender closer to full private ownership after its state bailout in the 2008 financial crisis.

As a result of NatWest buying back its own shares from Britain's Treasury, and the government's sale of shares in the open market, the state's ownership of the bank has gone from just under 38% in May to 19.97% on Monday, the bank said.

"Returning NatWest Group to full private ownership remains a key ambition and we believe it is in the best interests of both the bank and all our shareholders,” NatWest CEO Paul Thwaite said.

With a stake of less than 20%, Britain's finance ministry will no longer be considered a related party to NatWest as of one year from Monday, the bank said.

That in turn would remove some administrative burdens from the bank, according to media reports in recent weeks.

Britain's new Labour government has said it would probably not proceed with the previous administration's plan to accelerate the return to private ownership via a one-off share sale to the public, but will continue with the overall objective of ending state ownership of the bank. (Reporting By Lawrence White Editing by Tomasz Janowski)