I really don't think it will be that easy mate. I was discussing my frame with the owner of my local bike shop. He is into his retro stuff and recalled having a guided tour of the Raleigh factory when they were producing these. He mentioned the fact that they had some type of small aluminium blocks within the frame joints which were heated up during manufacturing. These would subsequently melt and seal into the inner contours of the frame lugs creating a really strong bond. I would imagine that removing one of these tubes would need lots of heat!
Saying this I am no expert and a good frame builder/refurber may possess the skills/tools to do this.