Rental arbitrage involves renting a property on a long-term lease and subletting it on platforms like Airbnb as a short-term let. It is legal in the UK provided you have explicit written permission from your landlord, as most standard tenancy agreements prohibit subletting without consent. You must also comply with local short-let regulations, which vary by area. When structured correctly, rental arbitrage can be profitable if your short-let income consistently exceeds your rent and operating costs.