By Iain Withers and Saqib Iqbal Ahmed LONDON/NEW YORK (Reuters) -British bank Barclays faces an estimated 450 million pound ($592 million) loss and regulatory scrutiny for exceeding a U.S. limit on sales of structured products, some of which have surged in popularity since Russia’s invasion of Ukraine. Barclays also said on Monday that it will have to delay a planned 1 billion pound share buyback as of the loss, which it will have to incur as a result of buying back the securities in question at their original purchase price. Shares in Barclays closed down 4% after the bank said it had oversol…