I rarely post here but in response to your question I think this would qualify as a tariff. As such it would challenge any trade agreements we have.
Such an action should result in a retaliatory tariff against the participating UK members in a sane world.
Corbyn doesn’t want a trade deal with the US, he wants supplication to the EU, but it doesn’t matter, he won’t get in. Deep down Labour know they are fked so they can afford to come out with a load of fantasy student political BS.