BS4 deals with section sizes, EN 10056 deals with tolerances.
Material standards are now EN 10025 or EN 10113
the old grade 43 is now grade 275 (275N/mm2 YS)
the old grade 50 is now grade 355 (355N/mm2YS)
there is/was grade 40 now grade 235 (235N/mm2 YS)
so the safest would be to assume the...