This Planning Portal news item
states the "secret" document was signed in 2003 and includes a quote from Tesco that the agreement "precludes the council from promoting an alternative council-owned site". The spokesman also states that it was routine and that "this is completely normal in these sort of property deals". Tesco would be submitting a revised application in "the near future". Well it may be normal for Tesco but it seems rather fishy to me.