I used a chromium intensifier in the 1950s. I had no success at all with really thin negatives like yours. I never tried uranium, and the only reason for suggesting it is that the BJ Almanac (1956 edition) states: For 'ghost' neatives, uranium is admirable. The formula given is (in metric units):
Solution A: Uranium nitrate (23 g made up to 1 litre with water)
Solution B: Potassium ferricyanide 23 g made up to 1 litre with water)
For use, take 4 parts of A, 4 parts of B plus 1 part of acetic acid (presumaly glacial acetic acid). After intensification, wash in several changes of still water until the yellow stain is gone. A 2 per cent solution of ammonium thiocyanate will remove any yellow stain.
I do not know if any of the commercial intensifiers available in UK are of the uranium type or of similar effect.
Even if you go down this route, I would not hold your hopes of success high.
Uranium nitrate (uranyl nitrate) is available from chemical suppliers. It is a nasty as are many photographic chemicals but not radioactive, as any 1950s schoolboy would know. The minimum order I have found is £66 plus vat and carriage. Concentrated acetic acid (even if not the old 'glacial') and uranyl nitrate are available from chemical suppliers like Sigma-Aldrich. The other chemicals are in the Silverprint list.
Johnson's of Hendon made uranium intensifier see: http://bit.ly/VEywAW
You will see there that it was recommended for thin negatives. Somebody out there may have an old pack they would be willing to part with.