Reform would replace the Tories as the opposition, the survey found, and force Labour into third place at Holyrood.
The SNP is on course to be the largest party after the election but could fall short of a majority, a new poll has found.
According to the Diffley Partnership, the SNP is set to return 62 MSPs after May 7 – three short of a majority.
The poll, conducted using the Survation online panel, would see Reform UK Scotland winning 19 seats across the country, becoming Holyrood’s second largest party.
Scottish Labour would return 17 MSPs, while the Scottish Greens would have 12, one higher than the Scottish Conservatives. The Scottish Liberal Democrats would win eight seats, the survey suggests.
The SNP continues to have a substantial lead on both the constituency and regional list votes, the pollsters found, at 38% and 29% respectively.
A fifth of respondents said they would back Reform UK on the constituency ballot, while 19% said they would do so on the list.
Scottish Labour received the third-highest voter share in the poll, with 18% of voters supporting the party in their constituency, and 17% saying they would do the same on the list.
Some 12% of survey respondents said they would vote for the Tories on each ballot.
The Scottish Greens would also receive 12% of the list vote, according to the poll, but only 2% of the constituency vote.
And one in 10 Scots said they would opt for the Scottish Lib Dems on the constituency vote, with 9% saying the same for the list vote.
Voters continue to be divided over Scotland’s future in the UK, the Diffley Partnership also found, with 52% saying they would vote Yes in another referendum and 48% saying they would vote No.
The Edinburgh-based firm found opinion was also split on whether election results would constitute a mandate for another referendum.
Some 52% of respondents said they believed either an SNP majority or a pro-independence majority after the election would count as a mandate for independence, while 48% disagreed.
Asked who they would prefer as first minister, 58% of survey respondents opted for SNP leader John Swinney over Scottish Labour leader Anas Sarwar, while 42% chose Mr Sarwar over the current First Minister.
Some 68% said they preferred Mr Swinney over Reform UK Scotland leader Lord Malcolm Offord, while 32% opted for Lord Offord over Mr Swinney. Some 60% choose Mr Sarwar over Lord Offord, compared with the 40% who preferred Lord Offord.
Mr Swinney also had the best favourability among respondents with a net score of -4, compared with Mr Sarwar on -19 and Lord Offord on -21.
Nearly half of voters (47%) say they would prefer a single‑party majority government following the election, with an SNP minority government being the most acceptable option to voters, with 42% favourable and 44% unfavourable.
Some 34% expressed a positive view of a minority Labour government, with 54% expressing a negative view.
Meanwhile, 52% of people said they had an unfavourable view of any governing arrangements with Reform, with 36% holding a favourable view.
Scott Edgar, senior research manager at Diffley Partnership, said: “This polling suggests a complex and finely balanced contest.
“While the SNP remain clearly ahead and on course to be the largest party, albeit short of an overall majority, support for the other parties is broadly dispersed.
“If these figures were repeated on polling day, Scotland would be heading towards a fragmented parliament, meaning relatively small shifts in support between now and next Thursday could have a significant impact on the final distribution of seats.
“At the same time, voters are divided on both the independence question itself and on whether a pro-independence majority in the parliament would amount to a clear mandate for another referendum.
“Attitudes towards minority and coalition arrangements are similarly mixed, suggesting that post‑election decision‑making will take place in the absence of a clear consensus.”
Results are based on a survey of 1,012 respondents from April 17-23.
Scottish Greens constitution spokesperson Patrick Harvie said the party was “delighted to see what would be a record number of Scottish Green MSPs elected to Holyrood”.
“It also shows that Scotland is on course to return a clear pro-independence majority,” he added.
“The Scottish Greens believe in democracy. If Scotland chooses a majority of pro-independence MSPs on May 7, then it is undeniable that Scotland should be given a choice on its future.
“It would be absurd for anyone to suggest that only one party’s majority counts, while dismissing the votes of people who back independence but choose a different pro-independence party.
“A bigger group of Scottish Green MSPs would ensure that mandate is used to demand better and push for a fairer, greener, independent Scotland. One that taxes wealth fairly, protects our climate properly, and puts people before profit.”
Scottish Tory deputy leader Rachael Hamilton said: “This is yet another poll showing the threat of an SNP majority is very real.
“They are on the cusp of what John Swinney has repeatedly said he will use to demand another divisive independence referendum.
“The best way for Scots to stop this nightmare scenario from happening is to vote for the Scottish Conservatives on their peach ballot paper on May 7.”
