Personal finance guru Martin Lewis has issued an urgent warning to anyone passing through an airport this summer. Holidaymakers have been cautioned that they will be making a costly error if they make a particular decision when they are ‘captive custom’.

Travellers heading abroad this year are already anxious about potential price hikes and disruption stemming from the situation in the Middle East. Mr Lewis, speaking on ITV’s This Morning, made clear that attempting to obtain cash while at the airport is a serious misstep.

He told presenters Ben Shephard and Cat Deeley that many people like to carry cash for purposes such as tipping – while others prefer using it to manage their spending more effectively. He said: “The worst place to get your cash is at the airport or at the ferry port or anywhere like that because they have your captive custom and the rates are horrendous”.

” The best thing to do is to use a couple of travel exchange comparison sites online. Now, the thing is, you have to be careful. It’s a combination of the exchange rate and the fee. So what exchange rate are they giving you? What fee are they giving you? You want that all combined. And that’s what the comparison sites will do.

“You’ll just say, ‘I want £600 worth of dollars. Who’s going to give me the most dollars for my £600?’ And that’s the way that they will work. So, that’s by far the simplest way to do it. Just get yourself on a comparison. But don’t wait till you get to your destination.”

He explained that comparison sites will examine perhaps 50 or 60 providers, whereas if you wait until arriving abroad the available options are unlikely to offer competitive rates. He said: “If you go regularly to the same price abroad and you know there’s a little fella and you know and he gives you great rates and they’re much better than the ones at home then it’s fine. But if you don’t have that specialist knowledge, do the comparison, take the cash before you go.

“I mean also if you really do want cash, if you got a specialist overseas card, you know you got a Chase card or something just put it in the cash machine abroad. There’s no fees and you get the near-perfect exchange rate. So that’s another way to get cash.”

Mr Lewis also highlighted that anyone spending money in European destinations such as Spain, Greece or France should always make one crucial decision when it comes to paying – or withdrawing cash. He pointed out that if people have gone to the trouble of arranging a card to work overseas, they’re actually adding substantial amounts onto their bills by making the wrong choice when asked whether to pay in euros or pounds.

He said: “If you spend, if you go to a machine abroad or you go to an ATM and you’re in Europe, let’s say, or if it says, do you want euros or pounds? What it’s actually saying is if it’s euros, do you want your card to do the conversion? Your card company. If it’s pounds, we will do the conversion. for you and then charge your card. So, that’s the decision. Now, we’ve just talked about getting a specialist overseas card that gives you a near perfect rate.

“Well, you want them to do the conversion. That’s why you got the specialist overseas card. And actually, even if you haven’t got a specialist card, even the bog standard pretty pants cards here tend to be better than the shop abroad doing it where they put a massive we can be six or 7% on the exchange rate. The same with overseas cash machines, which can also add a fee on top, but what happens is basically you put, let’s say, you’re in a cash machine abroad, and it’s saying pounds or euros, and you say, as I will absolutely do. I go I want euros please and it says are you sure you’re that we won’t do the conversion are you actually yes I want euros are you sure what are you doing.

“They are desperate to persuade you to let them do the conversion because they make a lot of money from it it’s the opposite of what they’re trying to push you to do is what you want to do so very simply if you’re in Europe and you paying on a card, paying euros if you’re in America, pay in dollars if you’re in Vietnam.”