The Mini was 50 in 2009. Once ever-so British, it was re-launched by BMW in 2001. Since then, more than a million have been produced worldwide and, as they say in their adverts, it's no ordinary drive, more a 'Mini Adventure'.

But some of you have found your 'Mini Adventure' is more a test of your nerves, because a crucial part of the steering system can fail without warning, and drivers can be left fighting for control of their car.

It happened to Heather Hinam as she was driving her five-year-old Mini around a roundabout. Heather said: "I came to a roundabout, went to turn the wheel and there was nothing. It was just like the wheel was rigid. So, I wrenched on the wheel as hard as I could. I just managed to get a little bit of movement in it sufficient to get me around the roundabout. It was very frightening."

Heather had bought her Mini from a used car dealer but she took it directly to her local BMW garage for repair. They said that her power steering pump had failed. That's the crucial part that has made manoeuvring modern cars so much easier, and it's so essential that if it fails, steering becomes extremely difficult - far harder in fact, than an older car with no power steering at all.

BMW's customer service told Heather this wasn't a common fault, which is surprising because we've heard from dozens of other Mini owners who've told us they've had exactly the same problem, and have had to fork out anything up to £800 for the repair.

Natalie Redford was shocked to find the steering on her six-year-old Mini became hard to handle on her journey home from work. As she turned right, she couldn't turn the steering wheel enough to make it around the corner and she mounted the pavement, narrowly missing a wall. "I was quite shook up - really shook up actually," Natalie told Watchdog. "Someone could have been on that path, and I could have gone into them, and there was nothing I could do about it at all."

BMW say that power steering pump failures are not common. When we rang 45 main dealers, 30 denied there was a common fault, 14 said they'd had a few problems and only one dealer said the power steering does have a tendency to go wrong. But if the problem really is as rare as BMW would like to make out, we were surprised to hear from one Mini specialist telling us he's doing a roaring trade replacing the faulty part.

Common problem
Matt Pike is an independent Mini mechanic, and a supplier of spare parts. He says he can barely keep up with demand for replacement power steering pumps: "At least 60 per cent of our regular customers have all had pumps changed. And we're getting at least two calls a day from people after power steering pumps because they're such a big failure. I'd say it's the most common problem we have with the Minis."

Some worried drivers have contacted VOSA, the government body responsible for vehicle safety. VOSA said they'd done their own tests, and were convinced that even if the pump fails, the car can still be driven safely.

Motoring expert Mark Brown is surprised the Mini's power steering pumps are failing so early in the car's life, and is concerned by the risks the failure can cause: "I'd expect power steering pumps to last virtually the lifetime of the car, with a few exceptions. I think that because of the number of reported incidents, and the potentially dangerous situation it can leave a driver in when the failure does occur, that we're getting into the realms now where a safety recall ought to be seriously considered."

BMW say that they're aware of an electrical issue which has the potential to affect the Electro Hydraulic Power Assisted Steering system fitted to more than 223,000 petrol-powered Minis sold between 2001 and 2007. This includes 175,000 Mini one, Mini Cooper and Cooper S cars sold between 2001 and 2005, 9,000 convertibles and 32,000 Mini Hatch cars sold in 2006 and 7,800 Mini Convertibles sold in 2007. BMW say that in January 2005 a modification was made to the pump supplied with all new Minis which virtually eradicated the issue.

In a statement the company said: "Mini UK strives to provide the best possible service to its customers and is concerned when they are not satisfied with their cars. We can appreciate that the issues these Mini owners experienced can be disturbing, but we have thoroughly investigated the cases of each customer, and worked hard to eradicate the issues described. As with all modern cars, power steering systems are an added support function that makes steering easier, especially at slow speeds, when parking for example. They are not an essential component of steering systems and cars can be driven perfectly safely without power steering assistance. All new Minis on sale today also feature new power steering mechanisms completely unaffected by these issues.

"However, Mini UK takes such incidents very seriously and has worked closely with the independent regulatory bodies who have liaised with us on the most appropriate route to take with this issue. Furthermore, we would advise that if any owner of a petrol-engine Mini produced between 2001-07 has concerns over this issue or has experienced a similar situation, they should contact our dedicated Mini UK Customer Service line on 0800 777129."