FGWRICH,
that is one of the ones I have problems with. I saw it twice, once going south then north. Just like your photos, one end has 50903 and the other end is the green 'JAMES HERRIOT' 59912 with old set number 180109 showing through the grime !
Andy S
The formations of all 180s are believed to be as below. Cars in bold are not in their correct set.
180101 50901 54901 55901 56901
59903
180102 50902 54902 55902 56902 59902
180103
50912 54903
55906 56903
59905 This set believed to be a collection of demic cars and is not in service.
180104 50904 54904 55904 56904 59904
180105 50905 54905 55905 56905
59901
180106 50906 54906
55903 56906 59906
180107 50907 54907 55907 56907 59907
180108 50908 54908 55908 56908 59908
180109 50909 54909
55913 56909 59909
180110 50910 54910 55910 59910
180111 50911 54911 55911 56911 59911
180112
50903 54912 55912 56912 59912
180113 50913 54913
55909 56913 59913
180114 50914 54914 55914 56914 59914
Not in a set: 56910