EU referendum, brexit and the aftermath

the opposite of demand side

I meant more literally, what is meant by the “supply side”?

My understanding of this is very basic, but IIRC supply side economics deals with taxation and regulation of production/producers, and free trade to allow said producers to sell their goods.

Therefore what the ERG say they want is deregulation, lower taxation, and no impediment to trade, whilst erecting the largest barriers to trade that exist outside of actual punitive sanctions (in the modern period), increasing taxation to make up for the drop in GDP due to said barriers, and we're in the process of realising that we can't deregulate because the markets we want to sell into are regulated, and won't (can't) buy our stuff unless it meets their standards.