The table, here, shows that an average A-rated washing machine, at 40C, uses 0.56kWh.
http://www.nef.org.uk/energyadvice/washing.htm
I've just drawn a quick sketch graph to extrapolate a figure for a 30C wash (and made an allowance for the AA-rating of your machine). That suggests that your machine probably uses around one third (or just over) of a kilowatt hour. Tariffs vary but a typical figure for the cost of 1kWh (including VAT) is around 12p, so that suggests around 4p or 5p per wash.
Chris