Royal Mail made a £3m profit in the first half of the financial year - the first time it has been in the black at this stage for five years.

But despite the good news, chairman Allan Leighton said there was a long way to go before the organisation achieved sustainable profitability.

The company, which is still clearing a backlog of mail following a series of wildcat strikes, said its day-to-day operations made a £55m profit compared with a £147m loss a year ago.

The financial figures covered the six months to September, before the strikes.

The company made a £542m loss in the first half of last year.

Mr Leighton said: "Crucially, Royal Mail has still not implemented key operational changes in most of the letters business.

"We did not earn this profit from efficiency gains through much-needed operational changes."

He said that Royal Mail was facing "very heavy" additional costs, including pay increases for 165,000 postal workers and an extra £100m a year to the pension fund.

Mr Leighton said the organisation had to earn almost half a billion pounds to keep the renewal plan on track.

"The key task for the rest of this year is to achieve the operational changes in Royal Mail as rapidly as possible by moving to a single daily delivery, improving the efficiency of the mail centres and streamlining the transport operation. We cannot afford any delay."