This commitment to help defend Finland or Sweden sounds suspiciously like the 1939 commitment to Poland, "...His Majesty's Government would feel themselves bound at once to lend the Polish Government all support in their power". We didn't even lend them the money they wanted for armaments.The treaties signed by the blonde gimp aren't worth the paper they're written on
Everyone quotes Lord Halifax at the time as saying the guarantee wasn't worth anything (no source though).
In a situation where (whether true or not) Russia sees NATO countries as a threat, and Ukraine means formerly neutral states want to join NATO, I'm not sure it really helps for anyone to say anything in public that aggravates the tensions (like airily talking about nuclear options). But we all know it's as much for his dwindling audience here as for any genuine care for Finland and Sweden.