[ubuntu] Repository update broken.

This moing my system gave me a security update that I installed.
Now I caot read or update Repositories, either from Update Manager or Terminal with $ sudo apt-get update.
I am getting the following messages:

The method driver /usr/lib/apt/methods/https could not be found. Is package apt-transport-https installed?

I get a similar message in Synaptic Package Manager so I tried to reinstall the package and I get the following:

admin@ubuntu_14:~$ sudo apt-get install apt-transport-https
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package apt-transport-https
admin@ubuntu_14:~$

So the package appears to be missing and I caot update the repositories to re-load it.

Can anyone shed some light on what's happened and can I recover from this?

Thanks

Nigel