@Firesuit
The default tariffs mentioned in the article are what the EU currently charges on exports from outside the EU- so what the UK currently charges on dairy imports from, say, the US. The assumption is that's what the U.K. would default to.
There's no obvious issue with the UK not imposing tariffs under WTO rules, except: 1) British farmers would end up hugely undercut- WTO rules would mean the U.K. Couldn't say 'we'll allow exactly enough imports to make up the shortfall with what we produce': if they open the doors tariff free then WTO rules they're open to the whole world. This could cripple British dairy farmers 2) the WTO does impose restrictions on the non-tariff subsidies the gov can provide to agriculture so trying to make it up to farmers in other ways would be a big issue 3) there are also issues with controlling quality and standards.
EU dairy farmers will be fucked by this, but despite what people seem to think, there's not much the EU can do. The British governments ineptitude in negotiations has been shocking. The EU is not going to roll over on the basic rules of being in the EU, but instead of focusing on what can be negotiated- and there are very specific niche issues that will in practice make a huge difference- the gov has focused on domestic grandstanding.
You may not believe the sun or the mail or the guardian are impartial- read Irish newspapers and see how the Irish government is preparing. They're taking their oil reserves out of the UK. They've built a new port. They've started hiring customs officials. The practicalities are being discussed in a much more impartial way- and, btw, this is all on the assumption the NI border won't become as issue, they've explicitly said they won't start preparing for that. These changes will happen, there are ways for the UK to work around then but they don't have the trade expertise- negotiating trade deals has been outsourced to the EU for thirty years- and they seem to have exerted exactly zero focus on the complexities instead grandstanding to the EU and imploding politically.
What is sad to watch is how this issue just hasn't moved on from a leave vs remain one- two years in, both sides should be engaging with how crap the gov is being in actually negotiating these issues, but the papers, the public, the people who should be holding the gov to account are still behaving tribally. I personally think the most likely option is a v soft brexit at the last minute, but none of these options have been adequately engaged with and whatever happens there will be a huge degree of largely unnecessary bitterness and misunderstanding attached to the process.