OK, the Boris part is not true, but as early as in 1899, British Parliament met to discuss “a submarine tunnel” which would connect Great Britain and the island of Ireland".

Probably the lawmakers were a bit ahead of the technology available then. Probably such a tunnel is technologically more realistic in these days.

https://www.newsletter.co.uk/heritage-and-retro/retro/through-archives-meeting-held-westminster-discuss-irish-channel-tunnel-2883403#gsc.tab=0