Can't find it mentioned elsewhere so thought I'd post this as it just popped into my head.

Jokey scene at the start of TIA showed the Doctor taking part in was pretty obviously an escape from a German prisoner of war camp.

I wonder if that will figure in the next episode?

I'll spoiler tag this bit - it's not a spoiler, just a thought but it means people can see the above part without having to read what I think it could point towards if - a big IF - the escape tunnel does appear in Kill Hitler...