Yes there is, I cant remember the exact paragraph, but I often quote it on a monday morning when my cheapskate seniors/officers come in.
I think its only a big thing if large sums are involved, people are using their rank to avoid paying it back or juniors feel forced to lend to seniors. (as I do on a Friday/Saturday night when everyone from the OC downwards "thought the night would be over sooner".
It is against the rules, and because I'm an 'orrible swot and have a lovely leather bound copy of the QR's sitting on my bookshelf, it reads:
"J5.082. Personnel are forbidden to engage in moneylending or to borrow money from their subordinates"
However, there is an Ammendment:
"Unless you intend to Double Bubble, in which case, go for it, and if the badmin can't repay in full, you simply stick a PRC355 on his flick and ask him where it's gone as he's had it for over a month now."
Don't invest in Savings Schemes, just Double Bubble a Squaddie!