If you already have Economy 7 electricity, then you can save substantially over a year by running the dryer at night (12 - 7 a.m. winter, 1 - 8 a.m. summer).
For example, a 3kW dryer run for 2 hours per load, based on a tariff of 7.54 pence per unit day, 3.13 pence per unit night:
Day: 7.54 x 3 x 2 x 1.05 = 47.5 pence per load.
Night: 3.13 x 3 x 2 x 1.05 = 19.7 pence per load.
If you were one of those families running one load every day, that adds up to more than £70 per year saved. In fact on some of the day tariffs which charge more per unit over a certain amount per billing period, the savings could well be greater. and keeping dryer usage to the night tariff might help reduce the cost-per-unit for other appliances too.
You would also be doing your bit to help the utilities to distribute their load more evenly and run more efficiently. About the worst time to start turning on a dryer in this respect is when you get home from work around 5 or 6 p.m. -- the time when electrical demand normally reaches its peak.