Thank you Sarah for the link you included in your response. It is a good site too with many, many maps. I was hoping to use a close up of an 1860s Mapco.net map of the streets of Southwark to compare a street layout with a modern map. Normally when wanting to make a comparison, I have always gone to the Mapco website which provided the excellent means for doing so.
It looks as though 'Midase' has interpreted the error message correctly: The site is either no longer available, is being upgraded or has been moved to another server. I am not sure whether this means it will be available in the future under a similar name so that it is clearly identifiable. Thank you too for your thoughts on this 'Midase'.
Trishanne, I too have Sarah's link in my Favourites and agree, it is most useful.
I am hoping to track down Mapco again though, I think it is hard to beat for people with London ancestors. Thank you all.