By Steven Shukor BBC News Website, London

Cabbies take around three years to pass the Knowledge exam

Black cab drivers, with their famed Knowledge of London's streets, have traditionally had the edge over their minicab rivals.

But the increasing use of sat-nav systems has led minicab drivers to claim they are almost as efficient.

The Knowledge, which normally takes three or four years' study to attain, involves remembering every street within six miles of Charing Cross.

While few minicab drivers would challenge the cabbies' pre-eminence in central London, they say sat-nav has put them on a level playing field outside Knowledge territory in the suburbs.

The BBC News Website decided to put this claim to the test to see if the guidance system had eroded the Knowledge's superiority.

Our examination, by no means scientific, involved hiring two cabs, a black cab with no sat-nav and a minicab with the device.

Of the dozen or so trials attended by the LDTA, the cabbies have won out on all occasions Bob Oddy Licensed Taxi Drivers' Association general secretary

Starting from the BBC London office in Marylebone High Street, in W1, we headed to Nunhead in SE15 - an 8.2-mile trip during the evening rush hour.

Driving the black cab was Bill, a retired police officer of 30 years, who had only recently passed his Knowledge test after only two years' training.

And in the red Citroen minicab was Somali-born Maya, who has only been covering central London for a month but has installed satellite navigation software in his car.

Bill left at 1705 BST and took us through Hyde Park Corner, St James' Park, Parliament Square, Westminster Bridge, over the Bricklayer's Arms flyover into Old Kent Road turning off into Pomeroy Street heading into Nunhead.

He took a small deviation around Nunhead's Victorian cemetery but quickly found his way, reaching the destination in 42 minutes, at 1747 BST. The trip cost �35.

Road works

While black cabs are also permitted to use sat-nav to help them on journeys to outer London, Bill said he was not convinced the technology would improve the quality of his service.

"Sat-nav won't tell me if there are road works on such and such a road, or that some routes work better depending on the time of day," he said.

Meanwhile, Maya set off at 1800 BST after inputting the destination address into his sat-nav device which estimated the journey time at an optimistic 27 minutes.

Minicab driver Maya's sat-nav directed him into a bus depot

His route took him through Victoria, a congested Vauxhall Bridge, Oval, Camberwell Green and Old Kent Road heading towards Peckham.

But near Peckham High Street, the sat-nav directed him to turn right a bit too soon, straight into a bus depot.

"How are we going to get out of here then," he said, letting out a chuckle as though it was not the first time sat-nav had led him astray. Good thing the meter was not running.

He completed the journey in 53 minutes - 11 minutes slower than the GPS-challenged Bill - but at �19, the fare was �16 cheaper.

The result was no surprise to Bob Oddy, general secretary of the London Taxi Drivers' Association (LTDA), who has been involved in several trials pitting guidance systems against London cabbies.

"Of the dozen or so trials attended by the LTDA, the cabbies have won out on all occasions," he said.

'Good test'

He added that the obvious flaw with most sat-nav systems was that they failed to recognise that the same route was not necessarily the best choice at different times of the day.

"A good test is to programme a route at 7am and then repeat the process at 7pm," he told the cabbies newspaper Taxi.

But John Griffin, founder of minicab firm Addison Lee, said: "A black cab driver who's done the Knowledge might know 8,000 routes through London but a sat-nav device knows 80,000 and that's a huge difference.

"Minicabs are now in their slipstream and things like satellite navigation, with us both using the same technology, will help us catch up."

Steve Wright, chairman of the Licensed Private Hire and Car Association, said sat-nav was a "great leveller".

"It brings private-hire cabs closer to the unique service of the black cab," he said.