LONDON (Reuters) - Japan's SoftBank Group (>> SoftBank Group Corp) made its first formal approach to buy UK chip designer ARM (>> ARM Holdings plc) after Britain voted to leave the European Union on June 23, a source close to the situation said.

The shock vote to leave the 28-member bloc has hammered sterling and hurt confidence in the British economy, but the share price in ARM has risen as the group's revenues are largely in dollars.

The source said the change in the value of the pound and the firm's share price meant the deal was around 7 percent more expensive than it would have been if it had happened a month ago.

The firm also briefed Britain's new prime minister, Theresa May, and finance minister, Philip Hammond, on the deal over the weekend ahead of the announcement on Monday.

(Reporting by Kate Holton; editing by Guy Faulconbridge)

Stocks treated in this article : ARM Holdings plc, SoftBank Group Corp