New research has shown most customers are failing to receive super-fast advertised broadband speeds.

While providers such as BT, Sky, TalkTalk and O2 are advertising broadband speeds of 20 or in some cases 24 megabits mbps, Ofcom, the industry reguator, says the speeds being delivered are just 58% of those advertised.

On average, Ofcom said, customers are being charged for a speed of up to 11.5 megabits per second (mbps), but receive just 5.2 mbps.

The problem centres mainly around the old copper wiring installed to carry phone calls. Those businesses and households on fibre optic cable services are more likely to receive the faster speeds.

Ofcom chief executive, Ed Richards said that in 2009, when actual speeds for broadband were 4.1 mbps, the average that those services were being advertised for stood at 7.1 mbps. This year, when people are generally getting 5.2 mbps out of their broadband, providers are advertising speeds up to 11.5 mbps.

"The gap between the average headline speed and actual speed has increased in this period even though the actual speed has risen."

Ofcom acknowledged selling broadband was not straightforward as there were many factors that could affect speeds. "There are challenges of wiring, line length and interference and so on. It's not as simple as taking an absolute standard product. It's a complicated product, more complicated than anyone imagined," he added.

Even so, it was the use of the phrase "up to" before a speed that was deemed unclear.

The survey found that on DSL services advertised as being "up to" 20Mbps, only 2% of customers got speeds in the range of 14 to 20 mbps. Of the others, 32% were getting an 8 to 14 mbps service and 65%, 8 mbps or less.

The news comes as Britain’s business suffered a blow when the government announced it was delying it promised nationwide roll out of faster broadband of at least 2mbps from 2012 to 2015.