Cheers for the positive comments folks latest update - tried it on coke and with a bigger fan from a bouncy castle as it seemed to struggle a bit with that aluminium fan.
as you can see, it got a bit hot!! This one is the one I made for my old man, who kindly gave me a sack of forge beans! The thing got so hot the bottom was glowing bright red! As a result, I've been and got some fire cement today and will make a lining for both using the cement and vermiculite which should prevent the steel from burning through, insulate the fire and shape the fire pot to concentrate the heat upover into the work. My old man has also loaned me a bouncy castle blower which has a bit more oomph about it. The combi boiler fan was OK with coke but it would struggle to get up to welding temperatures. He's also made us both improved flaps (ooh-err!) for the clinker trap from aluminium plate with brass counterweights (his scrap bin is a LOT posher than mine!).
I also got my anvil back today from it's long term loan, much to the delight of my three-year old apprentice who got her first hammer today:
she's definitely my daughter, there's no denying her lineage!