This back lane leads from the Bigg Market, which can be seen at the top of the street here. The other end connects with Westgate Road. It dates back to medieval times and probably means a muddy winding lane.
Newcastle's 'new' co-op was built on Newgate Street in 1932. Although 'art decor' in style, it gave more than a nod to Egypt where Howard Carter's discovery of Tutankhamun's tomb had just taken place. See http://www.timmonet.co.uk/html/newcastle_co-op.htm