Some restaurants will say at the time of booking "Oh, we need the table back by 9PM." That's the less-than-polite warning to say there is a time limit. At this point, I will be thinking "I am going to spend a reasonable amount of money at a top restaurant and you are telling me I only have 120 minutes to eat my meal?"
It is ridiculous and I have only experienced this in London - not anywhere else. Don't get me started on "why" restaurants do this. Typically, a sweet looking waiter / waitress will approach your table after dessert and ask whether you would like to take "coffee in the lounge". This is the code word for "your time is up!" Recently, I came across the phrase: "Gentlemen, I have arranged your coffee at the lounge, would you like to retire there now?" at Gordan Ramsay at Claridge's in London. So what could you do in such situations?
Excuses to hang around:
"Sorry, I don't drink coffee."
"Oh, I really like to have another dessert / cheese course. Can I see the menu please?"
"Is your lounge non-smoking? I am allergic to smoke - surely you would not like to organise an ambulance for me."
"Excuse me, did we ask you to arrange anything of the sort?"
"Is this how you earn your 12.5% service charge?"
"Are you asking me to leave this table because you have not made enough money tonight?"
"Now, if you were in my position, what would you be thinking?"
Remember, they owe you for your custom, not the other way round.