It all started with my sister Sarah. She'd grown sick of her ageing Fiat Punto and Henry and George's elbows were growing so fast that whenever the family went out, it was tears before the first lay-by. Sarah's heart was set on a Golf, so she persuaded her husband Gary - because Gary is a bloke - to go with her to the local VW showroom.

She took Gary because Sarah is one of the 80% of women who feel they need to enlist the help of a male partner or friend before they are ready to walk through a car showroom door. Many of these suspected that if they bought alone, they may not get a good deal, though the findings, commissioned on behalf of Duckhams, stress that women often lack confidence because generally they have less technical knowledge of cars than men.

The salesman who dealt with Sarah and Gary sounds like he was the spit of Swiss Tony from the Fast Show. He asked Gary some questions, then he asked him some more and, while Sarah pogoed up and down in his line of vision, she remained invisible. Yes, the car was for her, but if she'd just keep out of the man's business of negotiating a sale, she'd be doing herself a favour.

Half an hour later, they had bought a Mercedes-Benz A class, spending considerably more than they planned to, but Sarah was happy: "The dealer asked me what I needed and he listened to me." And it would have been a he - the latest figures show female sales staff make up just 30% of the 386,000 employed in UK car sales. So even though 42% of cars are bought by women, it's not surprising that many consider forecourts and showrooms to be no-go zones.

But is this perception right? To find out, I agreed with What Car? magazine that I would go to 10 dealerships to find out how much of a discount I could get on various new cars. Then What Car? staff reporter Sarah Cutler would go to the same places to see what sort of deal she could get. I said I was a self-employed professional, that I was in a position to pay for the car in full before driving away, but that I'd be interested in any credit schemes if that would mean saving money. Sarah made out that her situation was similar to mine. I visited all dealers before Sarah.

First stop was Northfield Audi in Tetbury, and we were after an A3 1.6 SE. The salesman, Richard Friend, was friendly enough but made it clear I would be wasting my time if I tried to haggle and that it would make no difference if I was paying with cash or credit. He did, however, run my details through Audi's Solutions scheme and went to great lengths to explain why I might be better off driving away under the terms of a repayment scheme. He also suggested that the extra for metallic paint would be money well spent when it came to trading the A3 in. There was no car immediately available for test drive, but one could easily be fixed up.

When Sarah went along, Richard Friend wasn't around but Malcolm Rance offered similar information. Paying cash or finance would make no difference, and he ran through the computer looking at Audi's Solutions scheme (which he was also enthusiastic about) and again there was no car available right then to test. But she was impressed by the service. No discount for either of us then.

Next it was to Dick Lovett in Bristol to buy a BMW 318 SE. Simon Cockram told me that the model I was after was one of the lowest depreciating cars on the market. He said the only discount available was 3%, and that was only given to bulk fleet buyers. He did suggest that a six disc CD changer could be thrown in with the windscreen price.

When Sarah went along Simon told her, as he did me, that only fleet buyers get 3% off. But when she said how serious she was, and that she could pay cash, he said he could probably get her that 3% off. There was no mention of a CD player so Sarah lost out to me on that, but her discount was worth £636. Sarah came away impressed that he'd seemed more keen to sell her a car than he had to me.

After a few more visits a pattern started to emerge. Far from being marginalised and undermined, Sarah was doing better than me, coming away from many dealerships with hefty discounts where I'd got just a few quid off. And I'd been thinking that we were going to nail these evil sexists who are obviously lurking behind every yukka plant, waiting to pounce and patronise the poor girl. "I haven't found any yet!" she beamed.

But then, just when I was thinking it was safe for a woman to walk into a showroom wearing nothing but a bikini and white stilettos, shouting "Ooh, can anyone help me with this handbag, it's so full of cash?", a vestige of the past struck. Rudy Paul was the man I'd tipped from our ten incognito visits as the best salesman of them all. He'd gushed so violently about the new Fiat Punto and £500 cashback deal that I'd virtually paid for one on the spot. I'd hidden my inside knowledge when he explained how good the car was to drive and played idiot when he narrated the best bits of a test drive. I liked him - the guy was a true professional, the right man to do business with.

When he saw Sarah, something went wrong: "I found him totally patronising. I told him which model I wanted but he pushed me to get the 16-valve model as it would perform better. He offered me the in-house deal of £500 cashback, but whereas he told Simon it was an in-house deal, he made me feel as if he'd cut £500 off just for me, just like that, no problem. When it came to discussing paint, he said, in light of the £500 off, he wouldn't throw in metallic paint - but asked me if I wanted to 'come and see the pretty colours'. He's a good salesman - I came away ready to buy a more expensive car than I'd planned. But I felt patronised and pressured, even if he did give me a lot of time."

I couldn't feel that sorry for her, considering her total saving was so much greater than mine. So was Sarah happy?

"Given that I made far bigger savings than Simon, I'd say yes. There were vestiges of sexism in some places, but I think we have to realise that, as a consumer issue, sexism can come from either sex and can be directed at either."

All of which made me anxiously search through my notes: of the ten dealers we'd ambushed, two had been women. Had Sarah got a better deal from them? Toyota exec Sharon Cross had offered me zilch off a Yaris 1.0 GLS supermini. Phew, Sarah had done no better. But Vauxhall saleswoman Sarah Cross offered me £540 off a Corsa 1.2 GLS, while for Sarah she'd coughed up £1020. I felt transactionally abused - and could only agree with What Car?'s verdict on our research: "If you're a man buying a car, you'd do best to ask a woman to negotiate for you". <P.The full report is in the May issue of What Car? magazine, on sale from Wednesday