I want a free download if a turn based strategy game which is similar
to Civilisation. I don't want a web based game but would like some
graphical interface.

Sounds like you want freeciv.

http://www.freeciv.org/

From the "about" section of that site:

"Freeciv is a free turn-based multiplayer strategy game, in which each
player becomes the leader of a civilization, fighting to obtain the
ultimate goal:
To become the greatest civilization. "

"Players of Civilization IIŽ by MicroproseŽ should feel at home, since
one aim of Freeciv is to have compatible rules. "

jeremymiles-ga

Search strategy: I knew this existed, so went straight to the site.

Asked the question at work and an answer was waiting for me when I got
home. Doubt I would have found this without resarcher!