i renewed mine last year from Singapore.
i down loaded the forms from the net then sent them off to cardiff by return courier pack.
sorry can’t remember how long it took , i seem to remember approx a week or 10 days.
you’ll need a letter stating your employed on a uk registered vessel from memory
i used to have a panamanian one, which i got at their embassy in singapore. it was really expensive compared to the uk one and probably ended up more hassle at the embassy. the uk application goes really smooth and fast as long as you submit everything they ask for.
i’ve actually only ever used my seamans book once for oilfield work. it was in Qatar and they stuck stamps all in the back pages which are intended for other things. It pissed me off cause i use the book for other things more akin to it’s proper purpose. that time half of us had seamans books the other half had work permits , on arrival i think it was?…the guys with the work permits had a smoother entry than us..
i friend also told me once (he had a legal case with an american company) that it’s quite relevant to a companies liability for you wether you are signed on as crew or passenger. if your under a seamans book the accident liability is limited by an international seamans aggreement or something ?
good luck anyway