Tell her your rich uncle has offered to release your inheritance when you get married, but your uncle has said on this occasion he’ll waive this requirement.
Your uncle is interested in investing in the gold but you’ll need to go up to Aberdeen to see him. Ask your lovely friend to send you the train fare as you can’t access your uncles inheritance until you prove to him in person that you’re serious about her.
Tell her – I should stop saying that – tell him that you’ll arrange for the gold to be transferred once you’ve spoken to your uncle. But say your uncle is very interested and is speaking with his bankers to arrange for a significant sum of money to be transferred as an investment.
Then get a PO box and wait for the £50 in the post for the train fare to Aberdeen (or whatever sum you decide), then go to the pub.