(Reuters) - Britain's accounting watchdog, the Financial Reporting Council (FRC), said on Monday it had launched an inquiry into PwC over its auditing of Tesco's 2012, 2013 and 2014 accounts.

Tesco said in September that it had overstated first-half profits by 250 million pounds due to incorrectly booking payments from suppliers -- a figure later raised to 263 million pounds, compounding earlier profit warnings.

The scandal led to the suspension, then exit, of several senior executives and sparked a series of investigations, including by Britain's Serious Fraud Office and possible investor lawsuits both in Britain and the United States.

"The FRC has launched an investigation under the Accountancy Scheme into members and a member firm in relation to the preparation, approval and audit of the financial statements of Tesco," the watchdog said on Monday.

It said the probe related to Tesco's financial years ended Feb. 25, 2012, Feb. 23, 2013 and Feb. 22 2014 and the first half to Aug. 23 2014.

PwC has been Tesco's auditor since 1983.

"We take our responsibilities very seriously and remain committed to delivering work to the highest professional standards. We will cooperate fully with the FRC in its enquiries," PwC said in a statement.

The FRC has powers to sanction accounting firms and their staff for failing to apply book-keeping rules properly.

Tesco said it had noted the FRC's statement.

"We will provide support to the FRC’s investigation," said a spokesman for the firm.

Shares in Tesco, down 45 percent so far this year, were down 0.5 percent at 184.6 pence at 1101 GMT.