The ruling on whether to disqualify the Thai Raksa Chart party is now scheduled for March 7. Wednesday's hearing comes about three weeks after Thai Raksa Chart shocked Thailand by nominating Princess Ubolratana Mahidol as its prime ministerial candidate.

Thailand's King Maha Vajiralongkorn quickly stopped his sister's nomination going ahead and the country's electoral commission has since petitioned the court to disband Thai Raksa Chart.

Thai Raksa Chart is an offshoot of the Pheu Thai party, which is aligned with former prime minister Thaksin Shinawatra. Various iterations of parties loyal to Thaksin have won every election in Thailand since 2001 but have been repeatedly removed by army coups and court actions over alleged corruption.

As Thai Raksa Chart's prospects hang in the balance, the leader of another popular opposition party, Future Forward, who is facing criminal charges will have his fate decided after the March 24 poll.

Future Forward was founded in March 2018 and is led by 40-year-old Thanathorn Juangroongruangkit, a billionaire who is wildly popular on social media and who – like Pheu Thai – has flagged cuts to spending on the Thai military, a proposal that has angered senior officers in the current military junta.

Thanathorn is facing prosecution for criticising the military government on social media last year, which would stop him – though not his party – from running. He also faces disqualification for a minor error in an online biography published by his party.

Thai prosecutors deferred the decision on whether to pursue criminal charges against Thanathorn on Wednesday.

Thanathorn, who has promised to end what he describes as dictatorship and to weaken Thailand's military, said before he met prosecutors that "we believe in our innocence. We believe in the rights of the people to criticise those in power, the fundamental rights of democracy".

The legal moves against Thai Raksa Chart and Thanathorn have reinforced questions over whether the election will be free and fair.

A senior member of Thailand's Democrat Party, former MP Kiat Sitthiamorn, acknowledged some Thais are nervous the military could stage another coup if the election delivers a result it does not agree with, such as an end to the rule of junta leader and former general Prayut Chan-o-cha, who is standing to retain the prime ministership, backed by the military-aligned Palang Pracharat Party.

"No one can determine that. If you listen to the army chief, he has denied that speculation. It’s a theory people talk about, but staging a coup is not something to be taken lightly," Kiat said.

Kiat told the Sydney Morning Herald and The Age his party's target was to win the first or second highest number of seats in the poll and then decide whether to form a coalition with pro-Prayut or pro-democracy parties.

"The Democrats could participate in a coalition after the election. In principle we have no problem working with any political party, provided there is no agenda for any particular person or family," he said, adding that Pheu Thai would have to distance themselves from the Shinawatra family.

The current ruler of Thailand, Prayut, came to power in 2014 after a military-backed coup but has seen his support slide in recent opinion polls as he has attempted make the transition to civilian rule.

The complicated electoral system introduced in a new Thai constitution last year means no party is likely to win an overall majority in the lower house and that a coalition government will have to be formed.

The new voting system has spurred the creation of a number of new offshoot parties, such as Thai Raksa Chart, which are designed to scoop up seats in the party list vote, rather than win seats in individual constituencies.

Despite the new voting system appearing to heavily favour Prayut being returned as a civilian prime minister, as polling day approaches the result is looking more and more uncertain according to the Australian National University's Thailand expert Greg Raymond.

"It is looking less likely that Prayut is going to be able to claim the prime ministership, unless Thanathorn is taken out of the race. That would open up a big variable – would votes flow back to the Democrats?" he said.

The Democrats, led by former prime minister Abhisit Vejjajiva, expect to poll well in and around Bangkok, and southern and central Thailand.