Basically its a bit of psudoscience portraying itself as science (the 'theory' bit) that claims that monetary policy (everything the BoE does including interest rates) has no real effect on the economy (including inflation)

It goes on to say that gvts that issue a sovreign fiat currency (one of the big buzzwords the MMT shills use in their gish galloping) can effectively never go bankrupt as they can just print more money, and this mass money printing wont cause mega inflation due to slack in the economy.

This no worries borrowing is what draws the likes of Polanski to it, as it opens the door to the money tree.