What is the equalent grade of En 8D in BS?

There isn't a direct, universally accepted equivalent grade between EN 8D (a European steel specification) and a BS (British Standard) number. The EN and BS systems, while covering similar materials, use different numbering and classification schemes.

To find an equivalent, you need to compare the chemical composition and mechanical properties specified in the EN 8D standard to those listed in various BS standards (likely within the BS 970 series which covers carbon and alloy steels). You'd need to consult the full specifications for EN 8D and relevant BS standards to make this comparison. This is best done with access to the standards documents themselves (often requiring subscription).

In short, there's no simple answer – a metallurgical engineer or materials specialist would be best suited to determine the closest BS equivalent.