hi paul i put them in a big garden tubb from WICKES added 10ltrs of bleach(i used b&qs own but any strong stuff should do) and topped up with water( about a ltr)
stirred it 2 to 6 times a day for 10 days and then added 2ltrs of bleach and left for 4 days( still stirring)
took them out twice during that time to wash and scrubb them in hot soapy water
i could have left them longer but they seemed white enough after that amount of time
you never know how white theyve gone till you compare photos when youve finished
im chuffed to bits with them but i still want skyways
spesh