If you're in the US or Europe, you'll probably get a better rate by exchanging cash into local currency at your destination.
This is so prevalent that it's common for new banks (or existing banks doing a push for their new current account) to offer commission-free overseas spending. But many of them have pulled the 'perk' after they've gained a large enough customer base. If I recall correctly, at least Halifax, Nationwide and Metro Bank have in the past offered accounts with no commission on overseas card transactions, and then changed the terms to the standard (2.25%-2.75%) after 1-3 years.