Corbyn's position here is vacuous as others have pointed out. It's barely different on the substance from the hard Brexiters.
It's using the semantic 'access' to sound like something we currently have ['membership'] and s'thing the Tories are prepared to give up.
Labour divides between those who don't like the capitalist club single market that blocks state aid.... [Corbynites]...
...and those who now feel immigration control has to be conceded and thus single market membership has to be given up.
They are thus not capable of opposing the government's position. They have 2 positions, both of which entail leaving the single market.
It's ok, unavoidable perhaps, having 2 rubbish positions. They are entitled to make those calculations and have those views.
[I frequently have more than 1 position on things in my own head]. But it's mendacious and confusing to present it as an opposing demand.