Well, it depends how much earlier you are aiming for.
Pre-WW2 is inconceivable. Defence concerns, however ridiculous they may seem now, ruled the roost. Any fixed link to France was deemed a security risk, and route for "ze evil Germans" to march through to conquer the UK. I've seen suggestions on here that the tunnel could be lined with explosives, to save security concerns, but I can't see that as commercially viable. Would you really want to invest in something that the military can blow up whenever they get slightly twitchy without even asking you?
It would only be the 1950s, in the aftermath of the Luftwaffe raids, that the security concerns were mostly negated because of the strategy of air supremacy and bombing.
There was a serious attempt to create one from 1964ish onwards, resulting in construction starting in 1974. But Labour pulled the plug due to anti-Europe concerns, against the backdrop of the EEC membership uncertainties.
That's the best opportunity for an earlier Channel Tunnel; the 1974 tunnel succeeds, probably opening around 1980. I think this was one thing that I posited in my 12:08 trains timeline several years ago.