alt Hacker NewsJust compare the British economy with that of France, or its own prior trajectory. Very similar economies, neighbours, one stayed in and the other left. France establishes there was no unexpected growth surge Britain missed out on. Continuing on the prior trajectory establishes there was no direct negative impact from leaving. Put them together and there's your answer.
Surely, somebody else has done that and either posted about it or even submitted an academic paper in some economy journal. Do you have any links?
[Ed.: nevermind, https://ukandeu.ac.uk/brexits-impact-on-the-uk-economy/ does what you described & it very much indicates an economic impact. You'll of course claim it's biased. Feel free to back that up with your own links to analysis.]