Britons are growing ever more pessimistic about the state of Brexit negotiations, with even diehard leavers angry with how the past year has gone for their cause, a wide-ranging new study has found.

The research by Britain Thinks found a significant decrease in the strongest supporters of Brexit and an increase in the most pro-remain voices.

Yet, the researchers also found little consensus for a way out of the chaos. Voters were generally negative about the prime minister’s Brexit deal and became even more so when the deal was referred to as “Theresa May’s”.

However, the study also found support for a second referendum had slipped slightly since June and a majority were deeply concerned about the prospect of no deal.

The analysis, carried out over the weekend, is based on the views of voters who participated in the thinktank’s “Brexit Diaries” study from 2017, which had mapped the opinions of 52 leave voters and 48 remain voters, as well as a poll of more than 2,000 voters.

The study had categorised voters into “diehards” who backed Brexit enthusiastically, “cautious optimists” of both leavers and remainers who were hopeful of making a success of Brexit, “accepting pragmatists” of disappointed remainers who believed the referendum result should be honoured, and finally the “devastated pessimists” who could not see any positives to leaving the EU.

Researchers found the number of “diehards” had shrunk significantly, from a third of the public to just over a quarter. The number of “devastated pessimists” has risen by 5% – overtaking the “diehards” as the largest number of voters.

Both the diehards and the cautious optimists in the study were negative about the prime minister’s deal, calling it “exasperating”, “uncertain” and “frustrating”. Overall, 44% agreed with the description that the deal was “the worst of all worlds”.

“A very diluted and watered-down deal attempting to please everyone whilst ending up pleasing no one,” one diehard voter said. “Unlikely to be voted through by MPs and therefore somewhat pointless in over-analysing.”

One of the study’s cautious optimists said the prime minister “has negotiated a worse deal than we currently had and I’m finding it hard to trust her”.

In the survey, 44% of British voters thought they would be worse off economically for the next three years, compared with 30% who did not, but 45% said they had higher hopes for the UK having greater sovereignty compared with 26% who did not. More than half of Britons – 56% – said they were worried about a no-deal Brexit.

One remainer told the study that the deal “may well have been the best it could have been at that stage given the lack of overall conviction of the UK wishing to leave and the EU wishing us to leave, it seems no one wanted the full exit and that is how the deal presents: half in/half out with no clear path covering future relations.”

Support for a new public vote on the deal is tentative, the study found, at about 49%, which has dropped from 53% in July. Predictably, the support differs widely across the different views of voters. A new referendum is backed by 79% of devastated pessimists, but just 18% of diehards.

One of the cautious optimists in the study said they had voted to leave but felt there had been “inadequate information” in the 2016 referendum. “I think another vote would be democratic. I think it is too simplistic to say that people voted to leave no matter what,” the voter said.