I have abandoned my project to put a front derailleur on the Birdy City. Getting the bottom bracket unscrewed to enable moving spacers from left to right side was proving to challenging as it's not just the matter of having the right tool but also holding the tool in place while applying sufficient force.I didn't want to make a mess of the bike only to verify that moving the spacers isn't enough to shift the chainline enough to suit the derailleur's range of movement. I wonder if Birdies built with a front derailleur are fitted with a longer crank axle in order to get the chainline further out.

I've therefore decided that the Birdy City will have to be rehomed who doesn't want to tackle big hills and have got a Birdy Rohloff on order (I was offered an attractive discount on a new one which helped make the decision). I'll be interested to compare the crank axle length on the two bikes as the Rohloff hub has a wider chainline than the Nexus hub.

Another pending project, to fit ergotec AHS handlebars to a Birdy so I have more variety in hand and body positions, will wait for the Birdy Rohloff which should be early next week.