2009 Ten Pence Mule struck with Lion reverse
While errors are not uncommon in modern coin production, mules are very rare - the Royal Mint has produced few in modern times, and the 2009 10 pence struck with the 2007 lion reverse is one of the very few circulating British mules that have been struck in the 21st century.
The 2009 ten pence struck with the lion reverse first came to light in 2015 when an example was sold by London Coins as lot 2020 in auction 150 for £750. It was reported to be one of two examples known. An example was offered for sale for £2,000 by a Swiss seller on eBay in 2016 but it is unclear if it sold or whether it was a different example. A second example was sold by Noonan's as lot 508 in the 7th June auction in 2023 for £1,300. An example was reportedly found in a 2008 mint set but it is unclear if it represents a third example: the first example at least seems to have been lightly circulated.
Given the unknown provenance of the coins it is hard to speculate on how the error occurred, but given the small number known and relatively late discovery it would appear to be the result of a genuine mistake. The 2008 10 pence pieces were struck with both the lion and shield reverses, so a mix-up with old dies is not outside the realm of possibility, especially as modern mints continue to use old dies past their inscribed year so as not to waste old dies. It is also unclear at to whether the coins can be found in circulation or sets or both.