Landing clearance may be issued if it the prescribed minimum is achieved. Although this a highly debated point in most of the countries except USA, landing clearances is issued only when runway is vacant and available for landing. In States they give landing clearance to no 3 landing aircraft.
If situation is tight pass on traffic information to landing aircraft, hold your breadth and give landing clearance. 99% cases aircraft will land safely, although flight crew would like to
kill you. After that prey to Him and try to forget and not to repeat the mistake