Everyone that I know is escaping that island. Why would you put yourself in a situation with bad weather, bad food, bad teeth, high inflation, and Little India everywhere you go? Before my visits, I have to watch 5 seasons of Peaky Binders just to prep myself for that working class English accent.
Listen, when you arrive in Vietnam, just tell the IO that you are running away from the freezing weather in England and they will give you a free 45 day entry.
No legit agent would do this for you. But you're in luck because all of them are illegitimate agents that poses as legit agents. Just ask them how much and they will "arrange" everything for you.