Martin,
I wouldn't go as far as to say impossible, for I have seen several good
examples of peaches grow in the North.
Last September I saw members of the Northern Fruit Group exhibiting
peaches at their show at Harlow Carr.
The variety -- Perergrine, a white fleshed peach which in the groups
experience is reliable against a warm wall.
In the Northern Fruit Group's leaflet "Suggested Fruit Cultivars for
the North" the variety Rochester is also recommended, with members
suggesting that it is a reliable cropper.
There are varieties of peaches refered to as Patio, which are grafted
on to a special dwarfing rootstock that will remain in a pot. The
rootstock is much more knarled than St. Juliean or Pixy.
Clifford
Bawtry, Doncaster, South Yorkshire