Larger grey adder (male?) and smaller so presumably younger brown adder (female?)
No interactions present.
Could well be female. Although youngsters often have this reddish colouration, which can change as they mature.
It was once suggested that these animals were a separate sub-species, tentatively called the "Dwarf Red Adder", apparently.
Lat/Lng: 49.9932, -5.2187
OS grid ref: SW694153
Windmill Farm Nature Reserve, Cornwall