Actually, she said it would cause inflation only if the central bank also successfully increases the money supply at the same time. I think Monbiot is suggestin

Actually, she said it would cause inflation only if the central bank also successfully increases the money supply at the same time. I think Monbiot is suggesting this as an alternative to that, rather than something to occur simultaneously. It's also worth pointing out that although central banks will always be able to produce the necessary liquidity, they have to take ever greater risks to do so. At the extreme, they could purchase each and every public and private bond in the economy, but then they expose themselves to the risk of default on those loans, which could result in severe future inflation. If they are unwilling to do this, then they will not be able to stop deflation. So although they can stop deflation, it's not clear that they will. Perhaps the most unfortunate thing about Monbiot's article is that he sees alternative currencies simply as a means to fight deflation, but Lietaer saw them as a way to create social capital. The benefit of a negative interest rate mutual credit currency is that it encourages a gift economy, rather than a competitive economy, and therefore builds social ties as well as financial wealth.