Originally Posted by Meerkat
Isn't it better just to use a UK bank cash card to withdraw funds from a hole-in-the-wall when abroad, or do high-street banks give even worse rates when doing that? The only country I can remember not being able to use my HK card is Bahrain, and the rates I get all seem miles better than what Travelex would offer.
Well, it used to be that withdrawing foreign currency abroad on your DEBIT card was the cheapest way.
Not anymore: 
many banks (incl. Barclays and Citibank) started applying the same charges for debit card cash transactions abroad as they do for credit card transactions.
I investigated this when I got a nasty shock in Italy this year: it turned out that withdrawing euros in Rome from a high-street bank ATM (some Banca Unione di Corruzione e Incompetenza) with Citibank debit card was only 0.3 percentage points cheaper than cash transaction at Travelex.
And while banks like giving you stories about how they apply rates better than cash forex rates for card transactions, there is still a spread.
Last time I checked, if you are actually using foreign currency abroad, buying it for GBP cash and pocketing BA miles is a very good idea.