Polling conducted in constituencies and on Eurosceptic issues of “potential strategic significance” to Ukip did not breach UK donation rules, an investigation has found.

The Electoral Commission said the research could have benefited the party but did not conclude it was done to help Ukip or that the party received any of the results.

The watchdog therefore ruled the polling was not a donation to Ukip under UK political finance rules, adding it would re-examine the issue should new evidence come to light.

The commission’s work focused on whether Ukip took “impermissible donations” from the Alliance for Direct Democracy in Europe (ADDE), a grouping which had MEPs from several countries but with a large Ukip majority, and the Institute for Direct Democracy in Europe (IDDE).

The investigation emerged after a 2016 European parliament audit found ADDE and IDDE misused more than €500,000 (£445,000) of EU funding, including on polling of interest to Ukip linked to the 2015 general election and ahead of the EU referendum.

Polling took place throughout 2015 in areas targeted by Ukip, including the South Thanet constituency contested by the party’s then leader, Nigel Farage, and across the home nations and in different EU countries. The total cost was estimated at €321,000.

The commission said: “While the ADDE and IDDE polling paid for by EPB (European Parliament Bureau) grant money was on topics relevant to Ukip, we did not conclude that it was done to help Ukip, or that Ukip received any of the outputs from the work.

“Therefore, the polling work was not a donation to Ukip under UK political finance rules.”

It added: “We saw that the polling work paid for by EPB grant funding was relevant to Ukip’s political position in 2015/16.

“It was carried out in geographical areas of potential strategic significance to Ukip. The questions were about attitudes towards the EU.

“The reports drawn up from the polling partly considered the data from a Ukip point of view. But we found insufficient evidence that the polls were commissioned to be for the benefit of Ukip and no evidence that Ukip received or benefited from any of this work.”

The commission also noted two ADDE contractors who worked on some of the polling also worked as Ukip campaign managers during the 2015 general election.

Bob Posner, the Electoral Commission’s director of political finance and regulation and legal counsel, said: “We undertook a thorough investigation that involved analysing a significant volume of evidence, as well as conducting interviews with a number of individuals.

“For an offence to be found, we must be satisfied that the burden of proof meets a criminal standard. We were not satisfied beyond reasonable doubt that Ukip took impermissible donations in this case.

“Should new evidence come to light that makes it appropriate for us to look again at this matter, we will do so.”