Curious detail: This was a UK choice, not an EU one. Other EU member states made it a requirement for their Parliament to agree. In the UK, the decision was taken to allow the government to override treaty scrutiny /1
Thus concerning CETA, Liam Fox as Secretary of State for International Trade decided to override the scrutiny reserve resolution of the Commons. Here’s the Chair of the European Scrutiny Committee /2 
The situation thus became that the UK - through its own choice - had disempowered its Parliament, while Belgium - through its own choice - had empowered even its regional Parliaments bbc.com/news/world-eur…
It is worth adding that even though the UK had opted to give its Parliament less of a voice than other Member States, EU Treaty Scrutiny was still stronger than treaty scrutiny under CRAG 2010. commonslibrary.parliament.uk/research-brief…
And the missing source: the inquiry into CETA treaty scrutiny data.parliament.uk/writtenevidenc…
The author of the report (and one of the top experts on treaty scrutiny in the UK) was @Arabella_Law
