Bethany Lewis is a nippy defender for Farsley Vixens under-11 football XI, but for the past six months her sharp eyes have been fixed on a mantelpiece digital monitor at her home in Leeds.

Its flickering numbers show the cost of the household's power, minute by minute, and if it climbs up beyond a couple of pence an hour, Bethany wants to know why.

Her vigilance, matched in 63 other homes on eight streets around Britain with the word green in their name, underlies a dramatic claim that simple good housekeeping could save Britain £4.6bn in domestic fuel bills.

"When I come in from school, I check the numbers," the nine-year-old says. "If they've gone up, I go to the telly to see if it's been left on, so that the video's on standby. If it has, I'll unplug it."

Thousands of similar small acts have put the Lewises' street, Green Lane in the suburb of Cookridge, into the lead in the national Green Streets competition. Halfway through the contest, which began in January, the gently sloping double row of 1960s terraces, semis and bungalows has cut costs by 29.32%.

Its seven rivals haven't done quite as well - Manchester is bottom with only 8.56%. But the Institute for Public Policy Research (IPPR) thinktank, which is monitoring the exercise for British Gas, calculates the £4.6bn - and a 20% fall in carbon emissions - from the eight streets' average score.

Energy use is moving rapidly up the political agenda as prices rise and put pressure on household budgets. Only last week one of Britain's biggest suppliers, EDF Energy, announced that it was raising gas prices by 22% and electricity by 17%. Its five major rivals are expected to follow with similar increases in price.

"We need creative approaches to energy efficiency like this, if the UK is to reach its CO2 reduction targets," says Matthew Lockwood, senior fellow in the IPPR's climate team. Bethany's mother Janine, an insurance team leader, agrees - but adds that it isn't rocket science.

"We've had a new energy-efficient boiler fitted as part of the competition," she says, "but what's struck us is that it's our behaviour which really makes the difference. Just the simplest things, like drawing the curtains later at night in the summer and keeping the lights off. Not putting the children's school uniform in the washing machine every day. Not leaving things on standby."

"And swapping our electric lawnmower for a manual one," adds her husband Ian, a copytaker with the Press Association. "It's just as good and it gives me a bit of a workout."

The Lewises have saved 27% on power bills so far - a handsome figure but one that is dwarfed by the Neysari family at the top of the hill. You won't miss their house, say Ian and Janine, because it's got great solar panels on the roof. Gleaming in the July sun, they have reduced the last six months' costs by half.

"We're heading for saving £500 on gas alone this year, half our previous bill," says Rebecca Neysari, an accountant currently at home with her hands full with three-year-old Cyrus and one-year-old Kiyana. The contest, which has equipped all 64 entrants with energy-efficient technology, has also fitted the house with a new water tank and boiler and individual room valves on all central heating radiators.

Friendly competition

Child power rules here, too. "Cyrus is always telling me to turn things off," says Neysari, wading through a roomful of mostly clockwork or push-and-pull toys. Group support plays an important part too; there's friendly competition between the eight households, but much more in the way of swapping tips.

"We meet regularly to see how everyone's doing," she says, adding that the one gizmo nobody in Green Lane likes is the one-cup kettle donated by British Gas. Halfway up the lane, immersed in her garden's ranks of plump peapods and swelling onions, Shirley Carter denounces it with vim.

"Hated it, I'm afraid," she admits. "I didn't consider it was properly boiled water, just not good enough for a proper cup of tea. I persevered for a while but we've gone back to the old kettle. But I always put lids on pans now, which we didn't used to do."

She and Neysari share Bethany's fascination with the digital monitor, the smallest but most significant of all the extras fitted to the contestants' houses, from Greenway Road in Cardiff to Edinburgh's Colinton Mains Green. "It shoots up when you've got something power-hungry on," Carter says. "Off you go, to find out what it is and do something about it."

Her list of tips includes solar-powered lights in the garden - for vegetable-watering at dusk, which was previously, expensively lit by electric lamps round the Carters' ornamental pond - and a security floodlight over their conservatory. Like Neysari, who now only uses her top oven for the children's meals, Shirley is also debating the "cooking Scrooge" gambit: turning the oven off five to 10 minutes before the end of the recommended cooking period, because it maintains sufficient heat.

Halfway through the competition, the IPPR is publishing three draft recommendations. In keeping with the Bethany/Cyrus approach, the suggested reforms are simple.

The first, says Lockwood, is extending the competition, central to the Green Streets project, by offering £4m annually from the Treasury as prizes for similar inter-town energy-saving contests. Secondly, IPPR suggests recruiting a national force of energy advisers similar to the British Gas experts who have been attached to Green Streets.

"It would be impossible to replicate this competition's ratio of one adviser for eight households," says Lockwood, "but if we had one for every 20 streets, that would be 10,000 advisers."

IPPR puts the cost at £500m annually, against the £4.6bn saving on national energy costs, which currently total about £23bn.

The final reform would repeat on a national scale the £30,000 British Gas has given to the eight streets to pay for new equipment such as the Lewises' boiler and the Neysaris' solar panels. Green mini-mortgages are suggested to fund, for example, a £524 package for cavity wall and loft insulation. A three-year loan at a 7% rate of interest would be offset by £395 annual savings in fuel bills, the thinktank says.

And the whole exercise is not a return to the shivering, primitive past, according to the Leeds energy adviser, Alan Pickard. "One of the most striking things has been how cosy everyone feels because of their new insulation," he says. "You don't have to suffer by saving energy."

How to shrink your footprint

Do

· Turn off all appliances on standby

· Use natural light as much as possible, fitting blinds for privacy

· Turn off oven five minutes before recommended cooking time

· Put lids on all pans

· Wash clothes at lower temperature, less often but with a full load

· Use dishwasher, not sink, but only full loads (stack carefully to avoid chips)

· Take fewer baths

· Use thermostats to the full and ideally lower by at least one degree celsius

· Fit valves on all radiators

· Lower hot-water temperature in summer

· Wash hair early in the evening and allow to dry naturally

Don't

· Overfill kettles

· Use a tumble dryer

· Use a hairdryer

· Let freezer frost up

· Draw curtains early and switch on lights

· Use powered equipment in small gardens

Fit

· An energy-efficient boiler

· Cavity wall, loft and underfloor insulation

· Solar panels

· Double glazing

· Draught-proofing

· Pipe-lagging

· Electronic timing