Red was the symbolic colour of socialism from the earliest times, and The Red Flag was the anthem of the British Labour Party from its inception until the Tony Blair era.

The people's flag is deepest red,
It shrouded oft our martyr'd dead
And ere their limbs grew stiff and cold,
Their hearts' blood dyed its ev'ry fold.

Then raise the scarlet standard high,
Within its shade we'll live and die,
Though cowards flinch and traitors sneer,
We'll keep the red flag flying here.

Leon Rosselson correctly forecast the trend in Labour politics as long ago as 1963 with his Battle Hymn of the New Socialists:

The cloth cap and the working class
As images are dated,
For we are Labour's avant-garde
And we were educated.

So raise the umbrella high,
The bowler hat and Eton tie,
But just to prove we're still sincere
We'll sing The Red Flag once a year.