taken from the highway code site.

Double yellow lines mean no waiting at any time, unless there are signs that specifically indicate seasonal restrictions. The times at which the restrictions apply for other road markings are shown on nearby plates or on entry signs to controlled parking zones. If no days are shown on the signs, the restrictions are in force every day including Sundays and Bank Holidays.

http://www.direct.gov.uk/en/TravelAn...ings/index.htm