In any prosecution for keeping a betting-house, it shall be prima facie evidence that a house, room, tent, vehicle or place is used as a betting-house—
(a) if any police officer or person authorised to enter any such house, room, tent, vehicle, or place is wilfully prevented from or obstructed or delayed in, entering the house, room, tent, vehicle or place or any part of it;
(b) if any such house, room, tent, vehicle or place is found fitted or provided with any contrivance for concealing removing or destroying any instruments of betting.