Just a thought, and apologies if this is said in the last pages (I'm still trying to get through it all without getting caught by eagle-eyed managers LOL).
Are we still looking for Allan's paternal grandparents?
There's a James Robertson on the 1861, born slightly later than 1843 - 1845 in fact. But he is born in Camberwell, like Allan. The other linking factor is that he (at the age of 16) is a 'Boy 2 Class' aboard the ship the Nile.
Once again, apologies if this has already been found, but could this be Allan's father on the 1861? It could help in finding his parents maybe?
Mads
xxxxxx
Update: Sorry, just finally managed to reach some kind of confirmation about this being wrong (circa P26 I believe). 'Pologies!