No EU referendum should take place until the laws around the use of social media and campaign funding have been significantly tightened, Britain’s elections watchdog has warned.

Bob Posner, interim chief executive of the Electoral Commission, said that six-figure fines were needed to deter campaigners from breaching election laws – far higher than the penalties currently in place.

“We would want to extend investigative powers. We would want some serious sanctions, because that gives people confidence,” Posner told The House magazine.

“We would want much speedier reporting after the event of all the financial spending. And we’d also want more transparency during the event. We want the ability for us to actually go into campaigns and get hold of their financial information during the event.”

His warning comes after complaints over the way data was used by Brexit campaigners during the 2016 referendum. Arron Banks, the biggest Brexit donor, was referred to the National Crime Agency last year over claims that “a number of criminal offences may have been committed” regarding his £8m funding for Leave.EU. He denies any wrongdoing.

Asked if he would be worried if a referendum were to be held without the law being updated, Posner said: “We would be concerned … because we would want there to be learning from the previous event, which would raise people’s confidence, and it’s difficult to think that it would be sensible for parliament simply to take the rules from the last referendum and paste them across.”

Updating the law could be done as part of the parliamentary process needed to approve a second referendum. The regulator currently has a £20,000 cap per offence on fines it can impose for breaches of electoral rules. But Posner said there should be “an ability in the really egregious cases for us to fine at a level that matters. If the fines remain too low – and I think they are too low at the moment – then the result is you’re going to get more cases in front of the criminal courts, which is harsh and difficult for people.

“So, you’re talking about in the hundreds of thousands of pounds. I think that’s right. I don’t think we as a body would be fining that regularly in any way at all. It would be reserved for the things that really matter, and it will be a deterrent.”

The commission had a series of “contingency plans” in place for a snap election, which some MPs fear is on the way later this year to resolve the Brexit impasse, he said.

Posner added that the commission would work with MPs to ensure that should a second referendum be approved, the process would be carried out “speedily” and in the “tightest possible timescale”.