The original, mark 1, version had round holes but children kept poking their fingers into the holes and getting stuck.
So the mark 2 version had oval holes.
The design is still seen all over Milton Keynes although some later ones are silver colour rather than black - and there are still a couple of mark 1 benches in situ if one knows where to look
Recently the area around Lloyds Court, the first part of the central shopping area to open, has been refurbished and modern versions of the original street furniture put back and some new Brian Milne benches with round holes, but bigger ones to avoid the stuck finger issue, have been installed.
If the OP wants to know where they are made try asking MK City Council.