Pontious.
Yes they do have 10 exits, but due to the overwing type they do not have an L3 or R3 drop down door.
It is only high Density config that have the #3 door fit.
By the way you have not been at Britannia since the start of 757 operation or you would have seen the leased aircraft they operated from GLA. This aircraft had overwing exits and was
G-BTEJ leased from Icelandair.
As they would say, Have a nice day now!!