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Asked about reports that the company was heading for losses of �800m this year, Mr Leighton refused to comment on the figure.

But he confirmed that the annual accounts, due to be published later this month, would show a record deficit.

"You'll have to wait and see for the results," he said. "Without any doubt they will be the Post Office's worst results ever."

In the interview Mr Leighton was pressed on Consignia's record on overseas investment.

It has spent �600m buying into other postal companies in Europe, but has been criticised for not revealing enough information on how the investments have performed.

Questionable investments

File on 4 revealed details of one deal in Sweden in which the Post Office invested �25m in a company, but pulled out only 18 months later and handed its shares back to the founder for a �1.

He went on to re-sell a stake in the company to the Norwegian Post Office for �5m.

Allan Leighton: "Still a bargain"

Mr Leighton said the investment programme was carried out before his time as chairman.

"In the scheme of things I can understand absolutely the strategy, though certainly the execution could have been better."

He said he was now carrying out a complete review of Consignia's investment strategy.

"For me at the moment it's let's get back to our core business; it's let's look after our people; let's improve our service levels.

"If we want to invest in things we want a return... and we have got to be much more conscious of the money that we spend."

He added: "Unfortunately the PR you get is the PR you deserve and unfortunately at the moment we are not doing many things right, and we are getting a right caning for it."

File on 4 is broadcast on BBC Radio 4 on Tuesday at 2000BST, and repeated on Sunday at 1700BST.