Signal K Installation fails

[Jsimonc]

Trying to install Signal K and it fails with the following.


----------------------------------------------------------
Building dependency tree...
Reading state information...
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 npm : Depends: nodejs (>= 6.11~) but it is not going to be installed
       Depends: node-abbrev (>= 1.1.1~) but it is not going to be installed
       Depends: node-ansi-regex (>= 3.0~) but it is not going to be installed
       Depends: node-ansistyles (>= 0.1.3~) but it is not going to be installed
       Depends: node-aproba (>= 1.2~) but it is not going to be installed
       Depends: node-archy (>= 1.0~) but it is not going to be installed
       Depends: node-cacache (>= 10.0.4~) but it is not going to be installed
-----------------------------
and so on.
Any help please