Hello David here,
The list of countries with which the UK has signed a trade agreement is growing almost daily. As at 13th March 2019, the latest information can be found at gov.uk/guidance/signed-
It seems that the UK government has announced that most products – (some 87%) imported after a ‘no-deal’ Brexit will be granted a full rate of duty which is zero. This makes a preferential agreement unnecessary at this stage for those products. However, we understand this may be a temporary measure – presumably to allow time for preference deals to be signed in the interim.