Have to agree with Ed, petrol is a last last last case option.
Try the Meguires Stuff or the Auto Glyms stuff. Most manufactures make tar removal products now days and the Halfords near me has a shelf dedicated to it.
cellulose thnners, white spirit, petrol (as said above, fades paint), penetrating oil (swifts liberty spray/wd40), tar remover. (dont recomend turtle wax if you ever wanna spray your car etc)