How to upgrade an economy seat ono a flight to the Caribbean Q. I bought an economy ticket to Jamaica. I want to upgrade to premium economy on the flight out, but my travel agent wants to charge me another £300. Is it better to wait until I get to the airport and buy an upgrade there? Keith Preddie, Surrey A. Last-minute upgrades have plenty of appeal to airlines that find themselves with empty premium seats close to departure: they get lots of extra revenue at little extra cost. For passengers, too, the prospect of a more comfort for a modest additional investment is seductive. The question is: how best to achieve the extra legroom and better service? British Airways has always been among the most proactive in the business. Lately BA has been sending out speculative emails to economy passengers on transatlantic flights a few days before departure, offering upgrades to World Traveller Plus for around £150 one-way. You can also enquire at check-in, though some frequent travellers say this works more effectively at the distant end of the route, rather than outbound from London. The staff in "out-stations" seem to have more flexibility to negotiate. For Virgin Atlantic, upgrades to Premium Economy are usually on sale at the airport. The airline often has a sign on the check-in desk with that day's price for a more comfortable seat. For a flight to the Caribbean, the current fee seems to be £179. However, before you hand over your credit card, weigh up the benefits of what you are buying relative to the cost involved. The catering and in-flight entertainment are the same as in basic economy; you are basically acquiring a bit more personal space. A large slab of your spending - £81 - goes straight to the Chancellor as Air Passenger Duty, because APD doubles for anything above basic economy class. It might make sense to save the money to treat yourself to a great trip in Jamaica - for example to the fabulous Bob Marley Museum in Kingston. If you have any cash left at the end of the trip, try for an upgrade at the airport on the way home. The extra APD applies only on journeys from the UK. So not only is the price of an upgrade likely to be cheaper (typically around US$200, or £130) - it will also be more worthwhile as you seek to sleep on the long haul home.