Sorry, for not being clearer. I was flying Karachi - Dubai - London in Business Class with my sister. In Karachi we were handed J class boaring passes for KHI-DXB but Y class ones for DXB-LHR and were told that we would be given our J class seats in DXB. This did not happen... so we were only downgraded on the DXB-LHR segment (to a pair of middle seats at the back of the plane)

Cheers