Some people on another forum (mostly housewifey types with the odd househusband) did an experiment and used no washing powder in their daily/weekly washloads for a month.
They used 1 tbsp of washing soda (very cheap) and a splash of fabric conditioner and did not pack the clothes too tight in the drum.
All of them reported there was no difference in cleanliness of clothes, the only thing missing was the 'smell of a fake meadow'.
Since the cost of Tesco Value washing powder has leapt up from £1 something for 3kg to £2.39 (it was excellent too - lovely fresh smell) I am going to try this when my current bag runs out.
I've been using a version of this laundry protocol for many years, and can endorse it.
It is particularly good with our new energy star washer.
We cannot use detergent powder, because of very hard water; powder just doesn't dissolve properly. Soda dissolves nicely, and has a great freshening effect on sour smells.
I use a few drops of laundry detergent directly on the toughest stains. If they look to be still there after a brief scrub with an old toothbrush, I add a few drops of peroxide. You can get a similar foaming effect by scrubbing with bicarbonate of soda followed by a splash of white vinegar. [careful when it starts to foam, dont have your eyes too close, heh.]
I've never used more than a few drops of detergent in a load of laundry. Since we have our own septic field, and so many nearby streams, we need to be very careful about what goes into our water.
Bicarbonate of soda and white vinegar in household cleaning are also better for our water than detergents and cleansers.
Do they sell this washing soda in supermarkets then? I suppose it would be well hidden to prevent people choosing it over their powder.
I never heard of it perhaps I know it as something else.
You can buy it here at Summer Naturals but even at 99p, once you add postage it's going to turn out as expensive as real washing powder! 
I may try asking in a chemist. I seem to remember my Nan kept some under the sink, I used to like to play with the crystals and feed them to my dollies.
Merry had the cleanest dollies in town!
I have something called Soda Crystals under my sink whcih mummy used to use for cleaning grease off surfaces. Like Kitchen worktops and sinks and cookers etc, I am still getting around to using it.
It is like big lumps of crystally stuff and takes ages to dissolve so wouldn't that damage a washing machine used to powder and liquids.
Perhaps I need to pre dissolve it.
1kg for 99p at Tesco so I suppose other supermarkets do it too. So that would be three quid for 3kg so stil dearer than Tesco value powder unless you use less weight in soda crystals.
I have a 3kg box of Fairy that I got on special offer for a fiver at the moment.
I got some T V powder (the one I like) delivered this morning and I'm pleased with that, but will keep looking for the soda in case of future washing-powder famine.
Fairy!! us down here in the cash-strapped South can only dream of Fairy..... A fiver wasn't bad but that is still 3 Milka Daim Bars-worth more than the value stuff.
merry is hooked on Milka Daim bars; she dreams about them