The Law of One Price (LOOP) is an old idea in economics. LOOP states that the same product should cost the same in different places, expressed in the same currency. The intuition is that arbitrage (buying a product where it is cheap and selling it where it is expensive) should bring prices back into line. Can LOOP help us understand UK inflation? Yes. I find EU prices have much higher explanatory power for UK prices than domestic cost pressures, and the effects of exchange rate changes last longer, but build more slowly than commonly assumed.