The former chair of Vote Leave has sidestepped calls to apologise for the campaign breaking electoral law over spending limits during the EU referendum.

Gisela Stuart, a former Labour MP, told the BBC’s Andrew Marr show that the official Brexit campaign's legal advice ruled their activities compliant, but regulators had found otherwise at a later date.

She added that Vote Leave had been “outspent” by Remain and that it had "destroyed some of the evidential basis people are asking for" after deleting its data.

Key figures from the campaign, including Conservative leadership candidates Boris Johnson and Michael Gove, are facing growing calls to account for illegal behaviour by Vote Leave.

It comes after the Electoral Commission confirmed on Friday that Vote Leave had dropped its appeal against a £61,000 fine for electoral spending offences during the EU referendum.

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Asked why Vote Leave had withdrawn its appeal, Ms Stuart told the Andrew Marr Show: "I think what it shows is we have been outspent at every stage of this process – whether it was before the referendum started and the government spent £9.4 million on a leaflet, during the campaign...collectively the Remain side spent more, and going to appeals costs money too."

When asked whether she would apologise for the organisation breaking electoral law, Ms Stuart said: It was in relation of one particular donation where the Electoral Commission interpreted the rules as that being acting in concert, which we had got legal advice which said it wasn't.

"So the key question is if anybody wants a second referendum then the referendum legislation as it stands, and the way the Electoral Commission and Information Commissioner interprets them, needs rewriting."

Asked whether Vote Leave stood by its previous dismissal of the allegations against the campaign, Ms Stuart said: "Our biggest problem in the end was that we destroyed all our data, and therefore some of the evidential basis which people are asking for."

She added that at every stage the campaign did its "level best to be in compliance with the rules".

"If they were interpreted afterwards in a way which was different from the advice we got at that time, then so be it," she said. "The regulator always has the final word."

Since the Electoral Commission announced that Vote Leave had dropped its appeal, a number of politicians have urged other key figures to apologise on behalf of the campaign.

Labour deputy leader Tom Watson called on Boris Johnson to recognise that the campaign acted illegally. “I’m sure the man who seeks to be your prime minister will acknowledge… Vote Leave broke the law,” he said on Twitter.

Independent Group MP Anna Soubry told the Guardian that Mr Johnson and Mr Gove should "provide a full and proper explanation" after the appeal was dropped.

She said that the idea that it had been withdrawn for lack of funds was "ludicrous".

Labour MP David Lammy has also called for an update on a police investigation into the Vote Leave campaign.

"Vote Leave broke electoral law during the 2016 referendum. They want this news to be buried. Do not let them get away with it," he wrote on Twitter.

Vote Leave was fined in July after the Electoral Commission concluded it broke legal spending limits by donating hundreds of thousands to pro-Brexit youth group BeLeave days before the EU referendum in 2016.

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The electoral watchdog's report found evidence that BeLeave spent more than £675,000 on the data analytics and voter targeting firm AggreateIQ, that should have been declared by Vote Leave.

Vote Leave initially appealed against the fine, claiming that its donation to BeLeave had been signed off by the commission and its findings were “politically motivated”.