If you come on tourist visa from Poland you don't have a visa in your passport. You have only so called visa support (they send it by telex to embassy in Poland from Libya). According to this number they give you visa at the airport. I've heard recently that they are even reluctant to give your passport back.
If your point is that you are supposed to go to Libya on tourist visa and there is nothing in your passport then the answer is yes - it is possible to enter Libya without actual visa.
Please note that tourist company or anyone alse arranging your visit should forward your visa support to the airlines so you would be admitted on the plane.
And as I said in the beginning. It's from polish experience. Maybe British procedures are different.
