Many thanks, @JohnB5677
I had my head up my proverbial...
FYI I randomly found somewhere in one of the TT tips links that if your taxes were paid in foreign currency, as mine were, that you must use "Forms Method" (or "Forms" + a word-similar-to-"Method," but I'm forgetting). So they obviously want me to go into Form 1116 and put the GBP value directly in (and therefore have nowhere to enter using Step-by-Step).
