Richard a few suggestions in a moment. But first what NOT to buy unless you have the filter assembly for it. These are for early engines that have no bypass in the filter mount, this bypass came into play if the filter became seriously clogged. There are a lot floating around like this that have a blind end.
Some of them look to be of recent manufacture.
Of course the Domestic Management Code 6M51 is incorrect it should read 6MT1 & in the good old days LV6/MT1
I believe these equate to
British Filters Part No.1003, Type LF2/31B or LF3.
The correct one for most of us is LF3F in LV6/MT1/BG/LF3/35 later codified as 6MT1/2940-99-800-8003
From 1992 LF3/35 was quoted as 6MT1/2940-99-800-8051
In my accumulated cross references I too have
Crossland 432 but also a later number B674D
I also have
Tecalemit Type FA2688 LV6/MT1/TT/FG2430 that suggests Type FG2430 as well, it was later codified as 6MT1/2940-99-950-3538
Confusing i'nit!