In general, there are two types of "blight", early and late (convenient, no?) This time of the growing season you are probably dealing with late blight. Caused by fungal spores, it will soon destroy your plant. There are a number of treatments, ranging from purely organic to more effective (in my opinion) chemical applications. There's a new product, however, available here in the U.S. just this year. The trade name is Serenade Max. It treats the fungii differently than the cornmeal tea/milk organic applications or the more chemically driven Daconil. Since Serenade is produced by AgraQuest, Inc., which is a mulit-national company, it should be available in your area. It's developed with QST 713, a strain of dried Bacillus subtilis which, organically attacks the fungii responsible.
Did you grow tomatoes in the same pot last year? Big no-no for pot grown tomatos. Additionally, don't water the plant by drenching the leaves... only the soil and then being careful not to splash the water, since this is where the fungus originates... Best of luck!