The Tory position on Brexit and Single Market access is terrible, the vagueness of their understanding of the EU terrifying. That shouldn’t disguise the fact that the Labour position is also terrible. Labour aren’t proposing to cut workers’ rights, and Keir Starmer seems like he’d be much better prepared than David ‘100 pages of notes’ Davis. Still, that’s a low bar, Labour shouldn’t be excused on Brexit just because they’re less terrible than the Tories.
John McDonnell has spoken about “tariff-free access to the Single Market”. The best way to be sure of achieving that is by being in the Single Market. An alternative could take months to negotiate, and given the UK’s weak negotiating position, would probably mean having to give up something in return. Even the best possible option would be a step down from where we are at the moment – Norway has access to the Single Market, but have to abide by EU regulations, which they have no say in shaping.