可否於其他國家買機票?

當然可以啦，但係你用咩passport?因為入境時可能要證明出境日期。
最好就買咗先出發啦。覺得貴的話睇吓其他公司。如果你買嘅機票有leg嘅就多數平D （即係要connection) . Emirates or Qantas usually have pretty good offers.

Also, let me remind you that it's usually more expensive for one way ticket than return. Although, there's a policy in most airlines that you need to use the tickets sequentially, for example: you have a return ticket of 1.LON-HKG 2.HKG-LON, the sequence of the tickets need to be used as 1, then 2. If you use 2. before 1. you may pay a penalty or even lose both of your tickets. If that company has that policy, consequence is the same whether you buy it on the web or find a friend in UK to get a ticket for you. Safe bet would be a one way ticket, perhaps with a connection.

1.可否於其他國家買機票?
梗係可以啦。
2.但hk買好貴,可否於uk 公司的web 到買
or 搵uk fds幫手買?
梗係可以啦，我自己都試過。