For many of us, the sight of a Post Office slip can prompt thoughts that there might be an exciting delivery.

But for some people in north Norfolk the mysterious slip has potentially been less exciting, after about 20 campaigning letters from Liberal Democrat Norman Lamb did not have the correct postage.

The health minister spoke of his frustration last night after he claimed the distribution company tasked with sending out his post failed to frank it.

He said: 'I realise how totally frustrating it is for people to get a card through the door saying go to the post office. It is so frustrating when it is not us who has done it and we paid for a company to get something delivered.

'I apologised to the person who tweeted and made it clear that if someone has paid the excess we will pay the amount we have to cover.'

Mr Lamb was contacted yesterday by Nicola Gray, who said she was from north Norfolk, saying: 'Well done @normanlamb for sending my 17-year-old brother junk mail and making us pay for the postage! He can't even vote for you!'

Mr Lamb said he had emailed those who had been in touch so the postage could be reimbursed.

He said: 'I am just sorry it has happened. There have been two tweets about it that I have seen.

'I am conscious that when you get the card through the door, you might half think it is something exciting. To end up getting a letter from me may not be what they are after.

'The serious point is they do not want to pay a penalty price for it and that is why we are so frustrated. I have to take responsibility and I apologise to anyone who has been frustrated by it.'