Labour would prefer the UK to become a full member of the European single market after the country leaves the EU rather than just having access to it, according to John McDonnell.
Speaking at a fringe event at the Labour conference in Liverpool on Tuesday, the shadow chancellor said Labour is "open" to arguing for full single market membership for the UK if it becomes clear during Brexit negotiations that it's possible.
At the Federation of Small Businesses event, McDonnell also said he doesn't see any economic benefit to leaving the EU, predicted that article 50 would be activated in late 2017, and accused Labour MP Chris Leslie of attention-seeking after he criticised the shadow chancellor's headline economic plans.
"At the moment we're arguing for access [to the single market] because we think that's a more realistic prospect, but it's an open discussion," said McDonnell. "We argued to remain full stop, so therefore membership is preferable but it's likely access is more realistic.
"However, part of this discussion, and trying to get some certainty with government, is to tease out the parameters of the negotiations that will take place."
Any country can trade with the single market, but membership currently includes free movement of people, common trading laws between countries, and not being able to set tariffs on imports or exports.
Labour leader Jeremy Corbyn sparked a row with some of his MPs earlier this month after his spokesperson said there were "aspects" of single market membership he would reject, but that Corbyn wanted "full access" to it.
McDonnell added on Tuesday that from "peeping down letterboxes and whispering through keyholes at Number 10" it seems likely to him that the government will trigger Article 50, starting the two-year process of leaving the EU, after various elections in Europe next summer.
Labour is currently laying the groundwork to work with the government for the Brexit negotiations which would follow, said the shadow chancellor, and working with sister parties across Europe to "change the atmosphere" between the UK and EU members.
Asked if he could name an upside of Brexit, McDonnell said: "I can't at the moment. One of the upsides that was argued for was that you'd have more freedom to maneuver as a government for intervening in the economy, but to be frank I think that was largely a myth.
"There are some upsides I suppose in terms of freedom [from] the idealogical approach that has been developed in Europe in recent years ... and some of the problems we've got around the secret negotiations around TTIP [Transatlantic Trade and Investment Partnership], but I thought we could conquer those anyway by reform within the EU."
McDonnell also ridiculed former shadow chancellor Chris Leslie who attacked his plan, unveiled at the conference on Monday, for a £500 billion investment program and the possibility of introducing a universal basic income.
Speaking after McDonnell's speech, Leslie said: “The worry that I have is this suggestion of £500 billion. I mean, that’s an awful lot of either borrowing or extra taxation.
"In order to raise it you’d have to double income tax. You’d have to double national insurance. You’d have to double council tax, and you’d have to double VAT as well.”
However, asked about Leslie's comments, McDonnell said: "In terms of Chris Leslie, I'll send him a calculator. In no way does [the investment plan] imply either increases in taxation or increases in VAT."
He added: "We're not increasing income tax and we're not increasing VAT and Chris knows that, but sometimes in the heat of party conferences you want to make a splash, don't you?
"Mind you I'm trying to play it low key."