First of all, Raleigh frames usually have a lifetime warranty and this might qualify for free replacement. That's your first and faraway your best option. Failing that next best is to have a pair of steel collars made and fitted around the BB shell on both sides to support the shell and keep it closed properly. You might be able to use a split collar like one of those pictured here which would be better yet. I've had success with the single split style.

With any collar you'll have to get a diameter to match the shell and file notches on the collar to clear the downtube, seattube and chainstay welds. You'll also have to file away some of the plate welded on the bottom also.

As I said at the outset, it should be handled as a warranty issue and I'd pursue that aggressively before moving to a repair.