The problem has now been addressed in a sense as certain experts have written to Royal Mail regarding these issues and have not received any reply. Either they are not bothered that major dealers and auction houses regularly sell these or the legality question was one of a more perceived problem than a real one.
These stamps are usually offered as singles or small multiple blocks, it is not often one sees them for sale in cylinder block form. In fact I have not seen them at all, that is until today.
Whilst browsing eBay I have come across a couple of lots which contained Training stamps in cylinder blocks of 6.
(left) 9p values with a varnished coating overprinted with black vertical bars. Cylinder 12 dot P17 block of 6. The same seller also has a 9½p block overprinted with black vertical bars. Cylinder 13 dot block of 6.
Both these blocks have a low start price of 99p. As these are not
catalogued, It will be very interesting just to see what they realise. *
Note* No one is suggesting that these are anything but what the seller describes them as, far from it, I think they are very interesting lots, but collectors should be made aware it has been said in the past"When buying training stamps be very careful as Machins in particular do not have the bars overprited, they have the bars applied by hand with something similar to a felt tip pen."