Royal Mail have seen profits rise despite falling revenues and strikes
Postal workers are leaving "Sorry You Were Out" cards when people are in, says an industry Watchdog.
Failing to deliver parcels is also a cause for concern.
More than half of Royal Mail customers questioned insisted they were home when cards were slipped through their doors.
According to a new national ICM survey for industry watchdog Consumer Focus, 55% of those questioned had experienced this problem. 23% say it has happened three times or more.
Janet Reed, a proof-reader from Coventry, told Panorama, "They shoved the red card through the door and I'd go chasing after them and saying 'where is my parcel?'
"I am here waiting for it to be delivered and their usual excuse was we didn't bother putting it on the van because you're never at home. Whereas, I'm always at home, I work from home."
"It shouldn't be happening"
Postal expert Robert Hammond of Consumer Focus told the programme, "Clearly there's either a failure in the service that they're providing or alternatively it's about the nature of their business and Royal Mail should be getting to the bottom of it."
The survey also found that, while most customers still think the service is good, a quarter felt that the level of service they were getting from Royal Mail was either average or poor.
An internal Royal Mail memo obtained by the programme revealed that parcels were being left in the office "without any attempt to deliver the packet" and warned staff the practice must stop.
Royal Mail Operations Director Paul Tolhurst says, "It shouldn't be happening
if customers tell us that it's happening, we will discuss that in the local office with the local postmen, and we will try and put that right. That is not what they should be doing, but of course it does happen, and I'm not saying that it doesn't."
A quarter of customers say Royal Mail service is average or poor
Traditionally the busiest time, this Christmas isn't bringing much cheer for the Royal Mail.
Its letter business is down, there have been damaging strikes and it missed its most recent performance targets for delivering first and second class post.
Lord Sawyer, who led the 2001 review of industrial relations within Royal Mail and found a culture of distrust and bullying, says little has changed now.
"The issue is about trust. These people don't trust each other, and until that is addressed, and that is changed, we will continue to see a decline in the business based on - unsatisfactory industrial relations."
Union and managers can't agree on how much mail there really is to deliver, crucial figures in calculating how many employees are needed.
The Communication Workers Union alleges that managers at the Royal Mail have been undercounting the amount of mail reaching local delivery offices, to justify further cutbacks.
A union representative from Kent, Darran McCann, said that CWU carried out a sample count of mail in their area. "What they're finding was quite alarming. Where Royal Mail was saying that we were getting in a tray of mail of about 155 items, we were actually getting an average of around 220 to 270 items."
He claims it has a direct impact on customers with fewer staff having to do more work meaning that postmen and women are setting off on their rounds later and later.
"We just won't be able to provide the service that we'd like to provide small businesses and customers", McCann told Panorama.
Panorama put the allegation that volume figures were being fabricated to Paul Tolhurst, Royal Mail Operations director. "I'm afraid I think that's utter nonsense. There is a very extensive process that's undertaken so that we get accurate traffic counts," he said .
"I can really understand how a delivery postman feels,
probably they're saying
look I used to deliver six bags of mail a day; I'm still delivering six bags of mail a day. The reality is, what they're delivering is probably four or five more packages than they used to, and 50 less letters than they used to."
Despite the ongoing problems faced by the Royal Mail its half yearly results have just been published and show a 4% rise in profits to £184m in the first six months of the year, despite falling revenues and the industrial action by some staff.
Panorama Can't Deliver Won't Deliver, BBC One, 8.30 pm, Monday 14 December 2009.