Yes wow, this could be quite the little earner. My bonus period has ended now though.
This is even better than the US mint for churning CC spend (no heavy coins to lug around), I'm a little surprised it has only just come up on here, although if it was widely exploited on FT then I expect they would have to look at shutting it down.
I don't suppose you could get through quite the same volumes as the Mint though, otherwise they would surely start to get suspicious of money laundering?
If you are earning 12.5x per £ then the volumes would be enough, but at normal rates I think it would be too much effort or too noticable.