em-dash and comma, which comes first

I am confused about the preferred way to combine an em-dash insertion with a comma occurring in the outer sentence. Until now, I had preferred to write:

The erosion responsible for residuals is less related to the material process of creation—e.g., rewriting in the sense of Mondrian or blurring the edges in the sense of Rothko—, but to the double nature of time.

Consulting another question on the web, I convinced myself that em-dash and comma are complementary and there is nothing wrong in combining them. However the example on that linked page indicates that perhaps the comma should precede the insertion, like so:

The erosion responsible for residuals is less related to the material process of creation,—e.g., rewriting in the sense of Mondrian or blurring the edges in the sense of Rothko—but to the double nature of time.

Is there any advice on which variant would be preferred in academic British English?

Solution 1:

Functionally speaking, the two em-dashes function almost like a set of parentheses, enclosing information relevant to the connected clause, but not essential to it. Therefore, they should be contained entirely within the clause they are connected to, which is to say, inside the comma, not outside it.

The second rendering suggests that the introjection is related to the last half of the sentence, not the first.