Among all the treasures in the vaults of the Bank of England, a spectacularly battered, zinc-lined leather case, soon to go on public display for the first time, has been carefully preserved for almost a century.

The tattered label sheds no light on its original contents, but identifies it as the property of one Captain Blair Imrie. A 1936 ledger, cataloguing some of the more eccentric objects in the bank's stores, describes it – not much more helpfully – as a "camel pack for carrying gold over deserts". But Threadneedle Street legend, passed on among generations of bank workers, insists the scruffy box has a surprisingly glamorous history, having been lent by the bank in the first world war to Lawrence of Arabia, when it was filled with gold supplied by the government to reward the desert Arabs he was recruiting to rise against the Ottoman Empire.

The box will go on display when the Bank of England Museum reopens to the public on Monday 31 March. Jennifer Adam, the curator, has also found some correspondence in the archives which hints at a closer relationship between the bank and Lawrence than anyone had suspected. Although there is no direct reference to the saddlebag, she believes the letters do suggest that the story that the box belonged to Lawrence could well be true, and explain why such a scruffy and ostensibly worthless object was kept so carefully....