I wanted to pass along a quirk I just experienced while booking one way Eurostar tickets from London to Paris for July 2017. I had been researching times and prices on my smartphone while laying in bed last night, and I noticed that the pricing was all in GBPs. No big deal, I'm handy with mental currency conversion so I was fine.
This morning I decided to go ahead and finalize my plans, and I logged into a browser from my laptop. When I did the search, the times were all the same, but now the pricing was presented to me in USD. Most importantly, the pricing was significantly higher, as clearly they were reflecting a higher currency conversion rate than is currently available. To make sure I wasn't just dreaming about what I had seen last night, I went back to my smartphone, where I had saved my incomplete search, and double checked. Sure enough, the pricing was still in GBP.
On the USD website, a one way adult ticket is listed as $87 for the time I chose. On my smartphone, the same ticket was priced at 56 GBP. That's an implied exchange rate over 1.55, which is significantly higher than what is available on the currency markets.
I rapidly completed my purchase of 2 adult, 1 youth and 1 child ticket on my smartphone. The pending charge on my credit card is a savings of over $60 vs. the price in USD on the website. My actual exchange rate was just under 1.26.
I'm not entirely sure why this happened, but I'd recommend anyone planning to buy Eurostar tickets check out pricing from a mobile device to see if they can get pricing in GBP. Your credit card is going to give you a much better exchange rate than Eurostar currently is.
Good luck!