For 16.04, this bug has been fixed in apt-transport-https 1.2.19, released Jan 26, 2017, so you shouldn't run into it again with the Ubuntu ttf-mscorefonts-installer 3.4 package, provided you update apt-transport-https to 1.2.19.
For 14.04, I cannot reproduce what you describe. On my own 14.04 machine, I am able to install Ubuntu's ttf-mscorefonts-installer 3.4 without any error. Your issue may have a different cause. If you can still reproduce it, please open a new bug report with as much information as you can give, and subscribe me to it.
Robin:
Sorry I couldn't reply sooner.
For 16.04, this bug has been fixed in apt-transport-https 1.2.19, released Jan 26, 2017, so you shouldn't run into it again with the Ubuntu ttf-mscorefonts -installer 3.4 package, provided you update apt-transport-https to 1.2.19.
For 14.04, I cannot reproduce what you describe. On my own 14.04 machine, I am able to install Ubuntu's ttf-mscorefonts -installer 3.4 without any error. Your issue may have a different cause. If you can still reproduce it, please open a new bug report with as much information as you can give, and subscribe me to it.