The Conservatives aren't having to answer questions about the details of their plan, because the follow-up question to them saying "well we won't sign over the NHS" is, "well how are you going to get the meaningful deep US trade deal that you are going to need to make up for the lost economic trade with Europe if you're saying large chunks of our economy aren't on the table"? But because for them they can just say "it's Brexit or no Brexit".
If we join the customs union, we wouldn't have any control over European negotiation of any of this, so, and it could just as easily happen under a TTIP arrangement.
Now, I'm wondering to what extent it is true that UK membership of the EU customs union but not the EU itself would give the EU negotiating power in which it could offer the NHS in future trade deals, for example TTIP-like deals with the US.
To make this an objective question, and considering the UK and EU have been exploring their divorce for a while now, I am asking specifically if this specific scenario (the NHS's position in EU trade deals with third countries when the UK remains in the EU customs union while leaving as a member) has ever been explored in the negotiations.
For example, this could have come up if and when the UK was exploring a stay in the customs union but with specific exemptions and the NHS's position being one of those exemptions. Another option could be the EU having proposed something in this direction to break the deadlock, as a way to keep the UK more closely aligned than the more divergent deals it has since negotiated, but not passed.