Every day our travel guru answers your travel questions

Q. My parents-in-law will be visiting us from Chile next year, flying from Santiago around June. Ideally they would fly via Spain, as that helps the in-laws in terms of both language and travel time. They will also be travelling to Europe, certainly to Rome. Any pointers re getting the best-value flight? Should they take the return flight from outside the UK to avoid the air tax?

Denis Fitzpatrick, Luton

A. Let's start with the long-haul stretch, to Europe. Cheap round-trip deals are available travelling by both the US and Canada, on airlines such as American and Air Canada. But the journey via Madrid is much shorter and only slightly more expensive. The obvious airline is Iberia of Spain. But the Chilean airline, Lan, enjoys a better reputation for customer care on the very long trans-oceanic flight. Lan (like Iberia) is part of the Oneworld alliance, which means you can connect easily with British Airways.

Next, as you surmise, the overall fare depends on the route they take back to South America. Air Passenger Duty (APD) will be £94 by then (it's £92 now) if they fly home direct from the UK, with only a change of plane in Madrid. They can save over £80 each in APD if they fly home from somewhere other than Britain. The way to do this is to put the Rome element at the end of the trip, and for them fly back from there. Then, their APD liability will be only £13 each for the hop to Italy.

BA's useful "multi-stop" facility on ba.com quotes a fare of around US$1,770 (£1,120) for a June trip that goes Santiago-Madrid on Lan, Madrid-Heathrow on BA, Heathrow-Rome on BA and the same in reverse.

The crucial thing is to make sure that the Rome-London-Madrid-Santiago journey does not involve a stopover of 24 hours or more in London - which would make it liable to APD and push up the price.

With careful timing, however, you can engineer a shorter stop in London. There should be nothing to stop them leaving the airport, so you will be able to see them once more before they return home.

Fares for the summer are likely only to increase, so best book now to lock into a reasonable deal.