40 million was a nightmare with overcrowding at all major tourist destinations, facilities airports and immigration offices. 80 million, if it were to actually happen, would obviously be twice as bad.
Boris will likely abstain. I doubt he will feature much in politics unless or until Labour win the next general election. If that happens, as seems likely, expect him re-emerge shortly thereafter.
My Thai wife and I were married in Taiwan 1990 after which we had our marriage licence certified by the Thai embassy in Hong Kong. This has been accepted by Immigration in Bangkok when applying for a visa based on marriage, and for subsequent extensions.