Unfortunately, if my experience here in the U.S. is of any reference, the "four small patches" are just the beginning of the problem. Wait until next summer when you drive in when the tires (tyres?) are hot.
I found that cleaning the surface of the floor, repeatedly with a pressure washer and solvent was the key. I finally got good adherence with scrubbing the floor with said pressure washer and using a lite application of muriatic acid and rinsing well with the pressure washer.
The muriatic acid is fairly corrosive, but used at 1 part acid to 20 parts water, it etched the concrete sufficiently to assure good adherence.
One site says: "...Masonry can be very alkaline, which makes for poor adhesion of paints, etc. Washing masonry with muriatic acid neutralizes the alkalinity, leaving it in optimal condition to accept paints and other coatings. When cleaning masonry with muriatic acid, a powdery residue is left on the surface. Once that residue is rinsed off, you are left with a very clean, coating friendly surface..."
Good luck!