Sorry Hadrian, never saw that programme. I know that the roots are all over the trunk, so they just sort of stand in the soil to keep themselves upright, so I'd imagine, if you can find a way of jamming the tree into the top of an old one, it should just grow anyway. What I'm not sure about is whether monty don was just using the old, dead one as a sort of pillar to put the new, shorter one on, or whether you're saying he sort of grafted the two together. I'd imagine, as the first one is completely dead, it's just a way of having a taller tree fern when all you've got is a short version, which are much cheaper to buy - it looks more mature because its sitting on top of a dead trunk. If he cut the dead one to sit the new one on top, that might have been just to make a level surface, or it might have been because the new one would meld with the old, I'm not sure. Time for you to experiment, I think, lol! And probably the experiment would be better done in Spring rather than now, at the beginning of winter.

My apologies for my earlier, disbelieving reply if you can make this work Hadrian! Please let us know how you get on. As I wrote a few minutes ago "You learn something every day".