The lead of GERB, Bulgaria's biggest party led by outgoing Prime Minister Boyko Borisov, has shrunk drastically, a fresh survey shows.

GERB would get 20.3% of the vote, while its main opponent, the Bulgarian Socialist Party (BSP) which was an opposition to the outgoing cabinet, would earn 18.4% of the vote if an early election were to be held shortly, according to a Gallup International poll. The smallest margin recorded since 2009 (when GERB triumphed with a big victory in a regular general election) between the BSP and GERB was in 2013, after Borisov had stepped down over street protests. Back then, his party gained 30.5% of the ballots, an edge of just 4% on the BSP's 26.6%.

The pollster says it conducted the survey by phone among 1007 respondents between December 19 and 21.

The figures also show a substantial boost in support for the United Patriots, an ad hoc alliance of the Patriotic Front coalition and nationalist Ataka party which ran with a joint candidate in November's presidential election. In a hypothetical vote, nationalists would garner 10.1% of the ballots.

The Movement for Rights and Freedoms (DPS) party would receive just 6.3% of the vote.

In the previous snap vote in October 2014, it earned 14.8% of the vote.

If Varna-based businessman Veselin Mareshki (a political newcomer who mustered 11.1% of the presidential vote) decided to set up a party, he would be backed by 5.2% of voters in the early general election.

Support for the Reformist Bloc (RB), the junior partner in Bulgaria's outgoing coalition government, has plummeted compared to the previous vote - at 3.3%, against 2014's 8.888%.

ABV, the left-wing party of President (2002-2012) Georgi Parvanov, would get 1.4% of the vote, after having jumped the 4% threshold in 2014.

DSB, the right-wing party of Radan Kanev that splintered off the RB, would obtain the same result.

DOST, the party of former DPS leader Lyutvi Mestan, would get a result below 1%.

Some 4.8% would go for the "I Do Not Support Anyone" option.

If TV show host Slavi Trifonov were to run through his own political project, he would obtain 12% of the vote, an experimental test of Gallup shows.

New projects led by DSB's Kanev and former Justice Minister Hristo Ivanov would receive 1%. (The survey was conducted just before Ivanov announced he was formally turning his project, Yes, Bulgaria, into a political party.)

The figures, however, may change drastically over the months to come as elections are not to be held before the end of March.