That's just the hint I needed... after a bit of searching the following worked:
sudo apt purge php7.0-json php7.0-sqlite3
sudo apt install php7.0-json php7.0-sqlite3
sudo apt install --reinstall php7.0-cli php7.0-cgi
sudo phpenmod json sqlite3
sudo service lighttpd restart
The 'Solution' from the following thread:
Thanks for the help everyone!