The son of late Agony Aunt Claire Rayner has hit out at Royal Mail, after a birthday card containing £100 did not arrive at his home address.

Adam Rayner, of Ashfield Avenue, Bushey, said he waited more than a week for a card marking his 50th birthday from his father Des Rayner, 85, even though it was posted first class.

The father-of-one said: "The postman handed me one of those revenue protection cards, which stated a Christmas card was waiting for me at the local sorting office, but it had unpaid postage. Of course it was my birthday card.

"It was unpaid by 9p, I believe that’s because it had fallen foul of the size limits, by being 186 x 188mm.

"While first class will go up to 100g and sizing of 265 x 165mm, my card was said to be too big by a tiny margin, about that of a thumbnail. So I had to pay a handling fee of £1 plus the 9p owed.

"Obviously Royal Mail needs to protect its revenue, but the efforts that they go to must cost more than £1.

"And as a punter I’m looking at paying ten times plus the bit that’s missing. It’s ludicrous."

Mr Rayner said when he was finally reunited with his card, all of the money was inside, but the whole experience has left a bitter taste in his mouth.

He said: "My dad’s a daft old codger for sending the cash in the post. There are many ways to send money - he really shouldn’t have sent it that way.

"But this is the season of goodwill. Royal Mail should think of the harm they’re doing, in my opinion it will be pensioners who fall foul of this sizing system.

"For 9p, I just think the misery and rage that this has caused, my poor dad was ready to write the cash off.

"Maybe Royal Mail could find a way to remind people of their sizing regulations.

"The weight used to be 60g on an envelope. Now it’s 100g. That’s a bar of chocolate, maybe with a few squares removed, you could send that ok. But not my father’s card."

Royal Mail representatives said customers are always urged to check they have attached the correct postage.

Spokeswoman Sally Hopkins said: "Surcharging is the last thing Royal Mail wants to do - especially during the festive period.

"Royal Mail does not make a profit on surcharges and the fee is simply to help cover the extra costs involved in handling underpaid items. "Ensuring correct postage is paid helps keeps prices down and ensures everyone pays the same price.

"The huge bulk of the tens of millions of items of mail we handle daily carries the correct postage and surcharging applies to a minute fraction. If there are any cases where an error has been made then we would refund the postage and administration costs involved.

"Customers are advised not to send cash in the post or, if they wish to do so, to use our guaranteed Special Delivery service for any items of value."