peepes i spoke to last night thought it might have become the "poole arms",
dug out 1861 census and found john, his neighbouring pubs were the poole arms on one side and the "portsmouth hoy" on the other side,
presuming the" portsmouth" became the" nelson arms",that places john in the pub between the two.
the nelson and poole arms are still there, so i think your britannia is either the hideous amusement arcade or poole marine centre,if my memory serves me right the last time i was down there[i was drunk] the marine centre still has its old facade and was'nt totally flattened.
you could try writing to SCAPLENS COURT MUSEUM just put poole quay for the address ,that will find it,they are bound to have a picture of the quay around that time,its a brilliant little museum and they are very helpful.
hope all this helps
worwood,whellock,griffith,lee,,card,randall,london/lambeth/rotherhithe ,east wickham.young,tooley,nevil,chipping norton.legg, cheshunt.
scott,smither,spencer,taylor, farnham;surrey. halfacre ,hants.