File

The attached file contains a rather clunky (but working) solution I made up myself. It requires a certain amount of M-code manipulation but it's not too advanced.

Now you can do all this with more advanced techniques like custom functions and List.Generate. Search on-line for 'split multiple columns into rows power query'. You may find similar or even clunkier ones than mine.

Just as an alternative, you can split the two columns into lists and make a table out of them, then expand that table - see attached sample.

Nice! @Velouria

Thanks, though I can't claim credit. (unfortunately I've forgotten where I first came across that trick or I'd give proper attribution)

Thanks heaps for both responses.
Velouria's is nice.  And simple.  Just how I like it.
That's not to take away from Riny's Clunker.  That was also helpful and introduced me to some concepts I hadn't considered before.

Thank you both.