Celia Lawson went metric last month. It was the need for some UPVC building material that finally saw the 81-year-old make her first purchase in centimetres. That and her numeracy studies at the Swadlincote learning centre in south Derbyshire.

“When I was at school we learned how to do the grocery bill and order the household coal,” she says. “I used to do everything in pints and quarts, feet and inches. So I started out on the course not knowing much, but then I studied measures and fractions, decimals and things. I got a certificate for that.”

Celia’s purchase puts her ahead of the game. The Government reckons about one third of all adults - 11 million people - waste money on DIY. Their inability to work out the floor area of a room - either in imperial or metric - means they miscalculate and buy excessive quantities.

Ending up with a spare roll of Anaglypta is not a serious hardship. Neither is being unable to work out the odds on a horse race, a calculation thought to present difficulties for one-fifth of adults. Real numeracy problems are not being able to understand your cooker dial when you have a family to feed. Or to tell the time when you have a job interview to attend. Or being charged astronomical interest by a loan shark.

The Department for Education and Skills aims to have helped 750,000 adults to do as well as Celia Lawson by the end of this year. But, given the size of the country’s numeracy problems, that amounts to small beer. Celia’s course is at entry level 3, the standard expected of a competent 11-year-old. Just over 8 million adults in England get by at this level, a Skills for Life survey revealed late last year. Another seven million are below it, and their inadequacies cost the nation about pound;10 billion a year, according to the TUC and the Confederation of British Industry.

Innumeracy goes hand-in-hand with poverty, ill health, debt and life on the fringes of society. Sixty per cent of workers whose numeracy is sub-GCSE earn pound;5,000-pound;10,000 a year, the survey of 8,500 adults found.

This compares with the pound;30,000 or more taken home by 53 per cent of those with GCSE-level skills or higher.

Finding maths impenetrable makes life hard. “If people haven’t got a facility with number it destroys their autonomy,” says Bob Fryer, adult education guru and chief executive of the new National Health Service University. “I am always concerned with people’s dignity and confidence and their ability to navigate a world which has got a lot more numbers in it than before.”

Many find it easier to avoid navigation altogether. More women struggle with numeracy than men: none of Celia Lawson’s friends will join her on her course.

“They seem to be frightened, think they couldn’t cope,” she says. “Younger people of 40 or so are also frightened, but mainly of making fools of themselves. I’ve got to the age - and you can call me eccentric - when it doesn’t matter.”

Fear is an emotion Bianca Von Ellis has seen at first hand. Bianca is project manager for Link Up in the city of Derby. It is one of 18 pilot projects funded by the DfES, recruiting volunteers to go into the community and help people with learning needs. In Derby’s more deprived wards, this can add up to as many as three in five adults who lack the numeracy and literacy skills of a competent 11-year-old.

“Most people know they have a problem,” says Bianca, “and don’t mind admitting if they struggle with maths, though they won’t say if they can’t write a letter.”

Overcoming their fears is not easy. “They don’t want to go to a college because it is a huge red-brick institution. They have to catch buses to get there and then they have to fill in forms to start the course. It is moving out of their comfort zone to go to college.”

Once persuaded into the challenge zone, however, the results are rewarding.

“Even just doing things like booking holidays, paying for what they have bought through a catalogue, working out interest rates and so on becomes easier. They will step out that little bit more.”

And they may well step out on the road to becoming agents of change in their community - “active citizens”, as Bob Fryer puts it.

“Numeracy is an important component of citizenship,” he says, “in terms of being able to fully participate, to fully engage, to be able to act as an autonomous being with confidence and self-esteem.

“We need to embed learning of numeracy within the practicalities of what people do and want to do. Then they are far less fearful and make much faster progress.”

Working out what adults want is a difficult business. It has driven some dedicated adult educators to “lurking”. This is their term for hanging out in local pubs, cafes and toddlers’ groups just keying into people’s needs.

People who might not enrol for a numeracy course, but might consider one in positive thinking. People for whom the local college might be intimidating, but the local primary school is not.

For Bianca Von Ellis, successful community education must be flexible, free and accessible - “in places where people are not afraid to park their car at night”.

Yet far fewer turn up for numeracy than for literacy courses, says Jan Eldred, senior development officer with Niace. Partly, she says, this may be because there is a lack of well-qualified and inspirational tutors.

Partly it is to do with people learning how to get by with the numeracy they have.

“It is a complex issue. Either we are not marketing it right or they don’t feel the need to be as great as many of us think it is.”

But without a feeling for numbers, she says, not only are people more vulnerable to being ripped off, but they are also excluded from joining the debate on big issues such as globalisation and climate change.

“So much is to do with measurement and percentages. If you don’t understand those, how can you understand the depletion of the ozone layer, for example? And if you don’t understand those, how can you help your children to get to grips with such issues? ’

For Bob Fryer, being able to give youngsters a hand is part of being an autonomous citizen and helps to break the dismal record of poor maths passing down through families.

It was thanks to family ties that Celia Lawson enrolled on her numeracy studies course at Swadlincote. Her grandson said his maths wasn’t good enough to let him study for an MA. She said it was and, to motivate him, promised to study maths herself.

Her grandson is now taking his MA in fine art and photography, and Celia is getting to grips with personal finance, time, distance and speed, money, business in the community, salaries and interest ratesI all before the end of June. “I may not get through it all,” she admits. “It is gardening weather now.”

Unlike 10 per cent of adults, though, she presumably won’t have any problems with the seed-packet instructions.