If I understand you correctly that you are considering betting on those horses which won their last outs, be aware of whether they have moved up in class and picked up additional weight because of it (as is done in the U.S.).

My horse won two weeks ago in NW2. He ran yesterday, handicapped by nine additional pounds (and another 1/16 of race) against more proven horses carrying 5-8 pounds less (because they had not won lately).

If the conditions affecting the horse did not change, your idea might work. However, there are many other reasons a horse may "bounce" (not run back to the previous start).