British BC plugs dont conform to any British Standard which is why they vanished from the market place when conformance with British Standards became mandatory for all electrical accessories It would have been up to one of the manufacturers to get them added to BS  the then standard for BC lampholders now replaced by BS EN  but presumably no manufacturer thought the cost of the effort worth what they would make in sales BC plugs can still be found in some other countries which use BC lampholders Occasionally they can be found for sale in the UK but strictly its illegal to sell them now