What happened
David Davis, appointed Brexit Secretary in July 2016, told the House of Commons he expected to have 'a comprehensive free trade agreement and a comprehensive customs agreement' ready 'within the first year or two'. He later admitted no impact assessments had been conducted on leaving the EU single market.
The government was split between 'hard Brexit' advocates (who wanted complete severance from the EU's legal structures) and those who wanted to maintain close economic ties. Theresa May tried to hold these factions together with the deliberately ambiguous phrase 'Brexit means Brexit' — which meant nothing and was intended to mean nothing, because any specific meaning would have split the Cabinet.
The result: the UK triggered the two-year clock before answering basic questions: — Should the UK remain in the customs union? (No answer for 18 months.) — Should the UK remain in the single market? (No.) — What happens to the 3.5 million EU citizens in the UK and 1.2 million UK citizens in the EU? (To be decided.) — What happens at the Irish border? (No plan.) — What replaces EU financial services passporting? (No plan.)
Negotiating without a position is not unusual in diplomacy — but triggering a two-year legal deadline without a position is. Every month of confusion about what the UK actually wanted was a month not spent on the detail of what would eventually need to be agreed.