I've read a few articles lately about Brexit (for example this one at The Guardian and this one at the BBC) that take it for granted that the tariffs and conditions set by the WTO would have to be enforced in the event of a no-deal Brexit.
I'm interested in what would happen if the UK Government decided to ignore those tariffs and conditions.
For example, the linked Guardian article claims that
At present crashing out of the customs union under WTO rules means there has to be a new border with the EU with customs checks. All planes, trains and lorries have to be certificated and checked for tariff liability and regulatory compliance
and the BBC article claims
Under WTO rules, after Brexit, cars would be taxed at 10% when they crossed the UK-EU border. And agricultural tariffs would be significantly higher, rising to an average of more than 35% for dairy products.
The specific numbers and claims themselves are not the focus of my question. What would happen if the UK Government left the EU with no deal, and also chose not to enforce WTO rules?