I have a Brooks B5N that was originally fitted to a mid range Carlton from the early to mid 1960s. Some of the other components from the bike indicated that it may be a post Raleigh Carlton, which would be consistent with the B5N being a special Raleigh, and perhaps export only model.
One LBS here in Sydney Australia has a similar Carlton with the same B5N saddle. The B5N features lacing holes on the lower edge. I would be interested to know whether riders used string, leather or other material to lace their saddles.
Rolf Lunsmann