Due to essential maintenance works, please note that users of the Operational Data pages of the nationalgrid.com area of the website may experience intermittent periods where the system proceeds at less than the expected rate of speed.  The works are scheduled to commence at 19:30 on 26 February 2009 and complete at 10:00 on 27 February 2009. We apologise for any inconvenience this may cause our customers and we will keep you informed of any changes to the above programme.