When Brexit formalities took place on 1 January 2021, the UK was immediately subject to new customs and trade standards, both by the EU as well as third countries that had trade agreements with the EU, which previously applied to the UK. The UK and Switzerland had been in negotiations for quite some time over how trade would work between the two countries post Brexit, so on 1 January 2021, when Brexit ensued, the UK-Switzerland Free Trade Agreement (FTA) immediately took effect.
Source Customs4trade
