Former Prime Minister Manmohan Singh on Monday held that demonetisation will have a "very significant reverse effect on the country's GDP" and it will be an important issue in all states going to polls.Releasing the Congress manifesto for the Punjab assembly polls here, he said the Narendra Modi government's decision to demonetise Rs 1,000 and Rs 500 notes had significantly reversed the country's GDP. "I have said in the Parliament about demonetisation having its effect on GDP and it has already been established. According to Central Statistics Office estimates (for 2016-17), the GDP growth will be 7.1 per cent as against the targeted 7.6 per cent. "But this estimate doesn't take into account the effect of demonetisation on the system. If (that is done), you will see a very significant reverse effect on the country's GDP," he said.Attacking the government which maintained that the measure will not harm anyone, he said it has already been established that it has affected National Income and GDP. Manmohan Singh contended that the note ban would be an important issue not only in Punjab but in the other four states as well which face elections. Apart from Punjab, Goa, Uttar Pradesh, Uttarakhand and Manipur will vote in February and March.