RotaryBrit

Recently noticed that it when i am traveling in a straight line end accelerate,the cars nose pulls to the left.Back off and it straightens up.its only a small amount but i never noticed it before.Only thing i have done is changed a rear tyre after a flat,but i think problem lies is suspension or linkages.Any one had a similar problem or got any ideas?
Any help would be gratefully recieved guys,
Rotary Brit.