On the majority of goods imported into the UK tariffs don't apply because they are imported:
1 From EU
2 From FTA partners at 0%
3 From developing countries at 0%
4 Under a tariff quota at 0%
5 On a 0% tariff rating anyway
The World Bank published a report on trade preferences a few months ago.
documents.worldbank.org/curated/en/655…
The top orange dot is the average trade-weighted MFN tariff. Preferences for FTA partners and developing countries pull this down to the green dot.
I have annotated it to highlight EU countries and some others for comparison
Note how trade preferences mean that the average trade-weighted tariff (green dot) for EU countries ends up *BELOW* NZ, Australia, USA and Canada.
The lower tariffs from 3rd countries mean cheaper imports for us.
Here is a table of average agricultural tariffs OECD countries outside of the EU, the UK/EU, and a few others for comparison. EU already in he lower half is lower still once preferences are taken into account.
USA on the left, UK on the right.
Source: numbeo.com/cost-of-living…
I have 't even hinted on the fact that no deal means no FTAs, so all UK exports will be subject to tariffs from 3rd countries under WTO, MFN terms. If we unilaterally lowered tariffs as you suggest, what leverage is there then for trade deals?