Yep - we're back on this old chestnut again.
If it wasn't for the fact that the consequences of this fixation with "free trade" was so damaging for Britain as a nation there would be some sort of delicious irony in the fact that "free trade" conservatives will be the authors of their own destruction. However, their destruction will also mean the destruction of this nation and its people.
Free trade does not exist. It is questionable whether it is even possible (or desirable) to attain free trade within a national economy, but it most certainly is not possible beyond national borders.
For free trade to exist you have to have identical conditions for trade between the two trading parties - not mostly similar or relatively close conditions - they have to be identical. If they are not then one or other party will have a "penalty" and the trade can not be free.
As I said, this is pretty hard to achieve even within the national context. There are still regional discrepancies and so trade is never really free within national borders - but at least you can have a single government that can make those conditions as similar as it is possible to be.
But when you are talking about two different nations with two different governments with widely differing approaches to trade then "free trade" is nothing of the sort - and if those conditions of trade offer one of those nations such a massive advantage that you can not compete with it then it is in your national interest to impose conditions on trade with that nation.
If you don't then you are effectively giving up on your national economy. Other nations will take advantage of that and plunder your nation for what they can get. They'll sell you whatever they can and buy up whatever they want - until you've got nothing left to offer them at which point they'll leave you and go elsewhere.