These two are as old as me! The 12-sided 3d design was first planned in the mid 1930s. Just twelve were struck in 1936, with Edward VIIIs head on, as test pieces. But there were never any more minted, because of the abdication. Only 6 of this original dozen Edward VIII 3d coins have been accounted for - if you have one tucked away, it is worth in excess of £30K!! The coin only came into common use when his brother ascended the throne.
When decimalisation happened, in 1971, these little babies vanished, but we did get the heptagonal 50p piece, and then in 1982 the smaller 7-sided 20p coins appeared in our purses. And the Pound Note went, and we got round £1 coins with "Decus Et Tutamen" engraved round their edges. This Latin phrase means "an ornament and a safeguard" and refers to the earlier practice of 'coin clipping' where criminals nipped off the edges of the coins in order to glean the precious metals. Back in 1971, cynics were saying it meant "Ten-and-tuppence, cos that's all a pound is worth nowadays"
In 1998, along came the round £2 coin. This was a first, being made of two metals.
The Royal Mint continually strives to beat the counterfeiters.
And today we are getting another 12-sided coin again, the new £1. Her Maj on one side, and a design of rose, leek, shamrock and thistle on the other. Designed by a sixth former in Staffordshire, it represents the four countries in our "United Kingdom". Which all seems a bit ironic, when you look at the rows over Brexit, Indyref in Scotland, and the troubles of the Northern Ireland Parliament right now...
Anyway, here it is. You have until 15th October to spend the old round ones. The Royal Mint have produced an informative little video.
If you really cannot wait to get your hands on a twelve sided coin, the RM have also issued a map showing the location of the banks which will be issuing them into circulation. I wonder how long they will take to roll into Dorset?