Curve and Multi-Currency Cards: UK

Two problems collide on every overseas trip. The card you want to use for spending is your Avios-earning Amex, which either isn't accepted or comes with a 3% FX surcharge. The card with the best foreign exchange is your Starling debit card, which earns nothing. The UK has a handful of tools that bridge the gap, with varying degrees of cleverness and risk.

The shortlist of no-FX-fee cards

Chase debit card. Free, 1% cashback on most spend, no FX fees. Probably the simplest baseline for anyone without bigger ambitions.
Starling Bank debit card. Free, no FX fees, no cashback. Standard "just works" option for foreign spend.
Revolut. Free tier or paid tiers, no FX fees up to a monthly cap, weekend FX surcharge. Earns no points by default.
Halifax Clarity credit card. Free, no FX fees, no points, modest interest if you don't pay it off.
Barclaycard Rewards credit card. Free, no FX fees, 0.25% cashback.

None of these earn airline miles. Hence the desire to stack.

How Curve works (and where it breaks)

Curve is a Mastercard that sits in front of your other cards. When you tap Curve at a terminal, it actually charges one of your underlying cards behind the scenes. The clever bit for UK points collectors: you can have it charge your Amex even when the merchant doesn't accept Amex directly. Amex sees a Curve transaction and earns Membership Rewards or Avios on it. The merchant sees Mastercard.

This works. It is also fragile. Three things to know:

Amex periodically blocks Curve. Personal Amex cards have been blocked from "Anti-Money Laundering" type transactions through Curve in the past. The current rules vary. Always test small first.
Curve has its own FX charges for weekend transactions and above-cap amounts. The cap on the free tier is modest; serious foreign spend needs a paid tier.
If something goes wrong, the chargeback path is via Curve, not Amex. Section 75 may or may not apply (untested in court, despite some confident blog posts). Treat as not protected for safety.

The stacking play, end to end

A typical "best case" UK setup looks like:

Daily UK spend on a points-earning Amex (BA Premium Plus, Barclaycard Avios Plus, Amex Gold), paid off monthly in full.
Anywhere Amex isn't accepted, Curve in front of the Amex, again paid off monthly.
Foreign currency spend on a no-FX card (Chase or Starling). Or, where you're willing to accept Curve's risks, Curve-front-of-Amex with the FX done on Curve's interbank rate.
One emergency Visa or Mastercard in your wallet that has nothing to do with any of this, in case all of the above go sideways.

Realistic outcomes

On £5,000 of foreign spend during a long summer holiday, a points-stacked setup using Curve in front of an Amex earns roughly 7,500 Avios (at 1.5/£) instead of the zero you'd earn on a Chase debit card. That's worth roughly £75-100. The FX rate is similar between Curve and Chase, both close to interbank. The points are essentially free upside if Curve cooperates.

The catch: if you trip a Curve or Amex rule, the cardholder usually loses, not the bank. Don't put a critical booking on the stack.

The boring alternative

For anyone who doesn't want the admin: hold a Chase debit card for foreign spend and accept that you'll miss the Avios. The opportunity cost is real but small. The mental overhead of running a Curve-Amex stack is also real and often larger than the points are worth, especially on modest annual spend abroad. Pick the level of optimisation that matches how interested you actually are.