1 {map with red dashed line going from Boston, via St Johns, to London}
2 Prof. Jones: First stop in London is St Pancras.
2 Monty: The British Library?
2 Prof. Jones: A little pie shop I know on the corner.

The map is from a wonderful online collection of historical maps: the David Rumsey Historical Map Collection. According to the website, the map image is licensed under Creative Commons Attribution-NonCommercial-ShareAlike by Cartography Associates - though it's almost certain, given my reading of the site's legal text, that this map is in fact out of copyright and in the public domain.

This particular map is actually from 1841, quite a bit earlier than the 1930s time frame of this comic, but it serves well enough here.

EDIT: This is a case of serious research failure, I'm afraid. Having been to St Pancras and seen the impressive British Library building there, I sort of assumed it had been in its current location since at least the 1930s.* In fact, the British Library as an institution didn't even exist before 1973! Previously, the national collection of books was held in the British Museum, in the Bloomsbury area of London.

Although frankly, if you were looking for historical accuracy in a mid-20th century period comic, you've really come to the wrong place.

* Yes, I know it's a quite new and modern looking building - I also assumed it must have been upgraded very recently. Hey, why go for one unsupported assumption when you can have two for the same price?