Bicycles decorated with BJP flags and Narendra Modi's image are parked inside the BJP headquarters in New Delhi on May 12

The BJP's Narendra Modi is set to become India's next Prime Minister, exit polls showed on Monday, with his Opposition party and its allies forecast to sweep to a parliamentary majority.Indian elections are notoriously hard to call, however. Pre-election opinion polls and post-voting exit polls both have a patchy record. ( India Sets New Record for Voter Turnout at Over 66% Research group C-Voter predicted 289 seats for the National Democratic Alliance headed by the BJP, with just 101 seats for the alliance led by the Congress party - which would be the ruling party's worst ever result. ( As National Election Ends, Narendra Modi's Poll Analysis on Twitter C-Voter said its poll was based on a sample of 166,901 randomly selected respondents in all 543 seats up for election. The pollster said its margin of error is +\-3 percent at a national level. ( Narendra Modi blogs on the conclusion of 2014 Lok Sabha Elections Another poll, by Cicero for the India Today group, showed the NDA hitting between 261 and 283 seats. A majority of 272 is needed to form a government, although that is often achieved with outside support from regional parties. ( The World's Largest Elections: 5 Qs and As Several national exit polls over-estimated the BJP's seat share in the last two general elections in 2004 and 2009. The ruling Congress party went on to form coalition governments on both occasions. ( Key Dates in India's Record-Breaking Election Marathon "We will only know if this 'Modi wave' has really happened after the election results," said Praveen Rai, a political analyst at the Delhi-based Centre for the Study of Developing Societies (CSDS), who published a report on exit polls last month. "It still might be more of a media wave, a manufactured wave."Uttar Pradesh, India's most populous state and a crucial political battleground, is particularly tricky for pollsters to forecast because it is a caste-sensitive state where some voters are afraid to speak frankly about who they chose, said Rai.Should Mr Modi fall short of a majority when the results come in on May 16, he will need to strike a coalition deal with regional parties.Mr Modi, has electrified the lengthy contest with a media-savvy campaign that has hinged on vows to kickstart the economy and create jobs.

© Thomson Reuters 2014

Yet much depends on the BJP winning enough seats to form a stable government that will allow him to push through his promised reforms.