Various
British Standard 497 - Specification for manhole covers, road gully gratings and frames for drainage purposes. Cast iron and cast steel

Download the standard from the British Standards Institute site (payment) https://shop.bsigroup.com/ProductDetail/?pid=000000000000084547

An example of a cover that carries the standard on the "ultimate manhole covers" site. From this lid the picture that appears in the general section was taken.
There are 15 manhole covers in the site that has this standard
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The ultimate manhole covers site

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