HUNDREDS of thousands of items of mail for the Chorley postcode area could not be delivered last year, Post Office chiefs have revealed.

And an astonishing six million-plus items were 'undeliverable' throughout the entire North West for various reasons.

Royal Mail is urging customers to prepare mail correctly before posting.

All these letters and cards -- plus more than 50 million from other parts of the country -- end up at the Royal Mail National Return Letter Centre in Belfast where 300 postal workers forward them to correct addresses or return them to the sender.

Royal Mail explained that sometimes the addresses are inaccurate, incomplete, out of date, illegible, or even omitted altogether.

Sometimes internal post is dropped into the mail by mistake. And, more often than not, there is no return address on the envelope which then has to be opened and scrutinised for clues as to the sender or the addressee.

A total of 633,000 items of mail could not be delivered in the Preston mail centre area which deals with mail in the PR, BB FY and LA postcode districts.

Royal Mail says its NRLC costs around £6 million a year to run, and that while it is free, it is not -- at 50p a letter -- cheap.

Centre manager Ray Kennedy said: "You would be amazed at the simple mistakes people make when they are posting letters.

"And it is strange that more than 30 years after the introduction of the postcode, there are still people and businesses who don't always use it and don't even put their own name and address on the back of outgoing envelopes."

Royal Mail says sentimental items, for example, are treated with "great respect" by sorters and that anything of value is sent back by special delivery at no cost to the customer.

Forty per cent of all successfully re-delivered mail gets back within three days.

Letters that cannot be returned are held for three months while any items of personal value are held for up to a year