As Sarah Boseley reported recently, a large-scale study into the effects of 20mph limits in London found that they reduced cyclist injuries by 16.9%.

And last week, the government announced it was making it easier for councils to bring in 20mph limits.

Some cities have already done so. One is Oxford, where I live.

The reaction from motorists (and those who represent them) has been interesting – and instructive for anyone who is hoping to see speeds coming down near them. Motorists' letters published in Oxford papers have tended to condemn the 20mph limits. They don't like them because 30mph (while it is far more likely to kill any children who toddle into the road) lets motorists get into the centre of town more quickly.

But the professionals have different arguments. In Oxford, they have been put forward by Mark McArthur-Christie, who chairs the local group of the Institute of Advanced Motorists, and Mark Strange, the chairman of the Oxford Driving Instructors' Association.

These arguments suggest that cyclists and pedestrians were the groups that needed restricting, not drivers – and that now drivers have been hit by the new speed limits, cyclists and pedestrians will take advantage even further.

First, the McArthur-Christie perspective. He tells the Oxford Mail:

"The most fundamental argument of all is that the council is now using speed limits in a way they were never intended to be used. Speed limits were intended to reflect the behaviour of the law-abiding majority. They were never intended to be used as a tool for speed reduction."

Just in case you're not clear on that: speed limits were never intended to limit speed.

Secondly, the Strange argument.

"When you look at the Highway Code it says to pass cyclists as quickly and as safely as you can, but if you have got cyclists who can pedal up to 20mph very easily, you can easily get cyclists passing you now."

As a driver, I had always thought the Highway Code was saying that if I needed to pass a cyclist, I should do so as quickly and safely as possible. And if the cyclist is going too fast for me to do it safely without breaking the speed limit, I shouldn't try.

But this senior driving instructor apparently takes it for granted that cyclists must be passed (and quickly).

I've always been painfully aware that there are drivers who think cyclists must be overtaken, no matter how little road there is ahead, or how fast the cyclist is going ... but I always thought they did it because they were inexperienced or thick. I'm glad to be put right.

The second part of the Strange argument concerns pedestrians:

"[The 20mph limit] is also encouraging pedestrians to walk out in front of cars, because they know you're going slower and they know you will stop."

Why this is a bad thing, Mr Strange does not say.

The issue is kept ticking over on the letters pages of local papers. "I suggest placing a citywide speed limit on cyclists of 10mph," writes one correspondent to the Oxford Times. How would it be enforced? "By setting up mandatory licensing of cyclists ... speed cameras augmented with face recognition technology or the number plating of cyclists or their bicycles."

It all adds to the gaiety of nations. But are there any sensible anti-20mph arguments out there? And if you have experience of 20mph zones, do you think they benefit you on a bike – as a 16.9% reduction in casualties would suggest – or are they bringing unexpected problems?