It has been hailed as “the show of the season”, selling more advance tickets than any other exhibition in Tate Britain’s history.

But it has now emerged that the opening this week of Van Gogh and Britain, the gallery’s spring blockbuster, went ahead only after a last-minute diplomatic scramble to assure European galleries that any masterpieces loaned to the exhibition would not get stuck in a chaotic post-Brexit UK.

The British and Dutch governments were both enlisted to assure lenders that their works would not be subject to hefty import taxes when they returned to the EU if Britain crashed out with no deal, the Guardian has learned.

The Tate show was also specifically raised among European member states as a problem that needed an urgent resolution, before the European commission circulated new guidance on customs rules – barely a fortnight before the exhibition opened – to settle nerves.

Van Gogh’s Starry Night Over the Rhône on display at the Tate. Photograph: Anthony Harvey/REX/Shutterstock

British museums and galleries have been warning privately for some time that uncertainty around Brexit was making European institutions nervous about lending their works. But anxieties were particularly acute about the Van Gogh show, as its opening on 27 March was just two days before Britain was originally scheduled to leave the EU.

“Going to the UK was never a problem, but some museums were a bit concerned – would their works be able to come back?” a Dutch government source told the Guardian. “They wanted guarantees that they would have their works back in time, and without having to pay high import taxes.”

The Netherlands and UK embassies in London and the Hague were asked to intervene and the two countries’ culture ministries brought on board, before, in the words of the Dutch source, “the EU fixed it”. Discussions with member states led to the European commission drawing up new customs guidelines in the event of no deal, which were circulated on 11 March. Paintings loaned before Brexit but returning after it can be treated as “returned goods”, the guidelines indicate, and will therefore be subject to “total relief” from import taxes.

A woman looks at the Sunflowers painting. Photograph: Stuart C Wilson/Getty Images

It has not been confirmed which museums were particularly nervous about lending their paintings – and which artworks, therefore, might have been missing. But one Dutch museum which has loaned 15 Van Goghs to the exhibition told the Guardian that “of course there were concerns”.

“You want to make sure [before you loan an artwork] that all your information is correct about what is going to happen, which of course is still not clear,” Wobke Hooites, registrar of the Kröller-Müller museum in the Dutch town of Otterlo, told the Guardian. “So we looked at all the different scenarios.”

Both the Tate and the British government offered guidance, she said, and the museum also sought assurances from Dutch customs and from the gallery’s shipping company and insurer. Ultimately, however, the museum was not one of those seeking assurance at the last minute, she said, having decided last year that even amid the uncertainty, they were prepared to take the risk.

“Of course we knew that Brexit would be there on 29 March, and that the exhibition would open two days before. [But] we wanted to support Tate Britain in their Van Gogh exhibition,” Hooites said.

Schoolchildren examine the painting La Berceuse, by Van Gogh. Photograph: Andy Rain/EPA

“We always make a risk assessment, that is part of our loan procedure, and in this case the risk assessment is a bit difficult to make because it is hard to know what the risks are. I’m not sure why, but we felt positive everything was going to be OK. Sometimes you just have to support [a fellow museum], and that was very important to us.”

A spokesman for the Department for Digital, Media, Culture and Sport said it had worked closely with Tate Britain “to provide reassurance to our Dutch counterparts on tax implications of the UK’s changing relationship with the European Union”, and said that Britain planned to continue the current system of tax relief for UK museums and galleries that loan works abroad after Brexit.

A Tate spokesman said: “No special provisions were needed, as loans to museums would not be subject to commercial tariffs. The relevant authorities simply reassured lenders that this was the case. All works were transported to us through our normal processes.”

• The caption to the second picture was amended on 29 March 2019 because an earlier version called it The Starry Night; it is Van Gogh’s Starry Night Over the Rhône.