I think a contender for the anthem could be "Hearts of Olden Glory"

There's thunder clouds
Round the hometown bay
As I walk out
In the rain
Through the sepia showers
And the photoflood days

I caught a fleeting glimpse
Of life
And though the water's
Black as night
The colours of Scotland
Leave you young inside

There must be a place
Under the sun
Where hearts of olden glory
Grow young

There's a vision
Coming soon
Through the faith
That cleans your wound
Hearts of olden glory
Will be renewed

Down the glens
Where the headlands stand
I feel a healing
Through this land
A cross for a people
Like wind through your hands

There must be a place
Under the sun
Where hearts of olden glory
Grow young

Runrig, especially the siblings Calum and Rory MacDonald who wrote the bulk of the group's materil are great ambassadors to Scotland and especially the Gaidhlig language. This song could be sung in both Gaidhlig and in English as the Scottish national anthem. I don't think the lyrics are strictly political, as lyrics such as Flower of Scotland would be.