Now is the original poster using the American terminology where we would say bottling? If so, my mother has preserved fruit by bottling for 60 years in the Vale of York which can't be so much above sea level. There one can assume that boiling point is 100 degrees C.

 I live at about 1500 feet above sea level but still reckon the same temperatures with no problems though I realize the officially boiling point is slightly lower. Whe on earth should the O.P be under sea level in North England (Tyne Tees Tunnel?)

I apologize if I have misunderstood something