What should I do if I have returned from the USA and found the exit portion of the immigration card still in my passport? I'm rather nervous about this causing a snag on my next visit. B Phillips, Birmingham

Sunday Times travel expert, Richard Green, responds: Biometrics shmiometrics ­ because for now, a bit of green card that someone forgot to tear out of your passport can trip up the whole US immigration process.

The form is called an I-94, which is white for passengers with a visa, or an I-94W, which is green if travelling without a visa under the Visa Waiver Program. Either way, it should be removed by the check-in staff when you are leaving the States.

If not, the authorities may not have logged your departure, which could mean that you'll be refused entry on your next visit, or if you travelled on the Visa Waiver Programme this time, that you might need to apply for a visa the next time.

To avoid this, you need to forward the card to the US authorities, along with a letter of explanation and proof of your departure. Send it to ACS Inc, 1084 South Laurel Road, London, KY 40744, USA ­ and not to the US Embassy in London, as they won't forward it on.

To prove you have left the US, you'll need a boarding pass for your flight out, photocopied entry or departure stamps from your passport to show that you entered another country afterwards, or bank and credit card statements showing transactions outside of the US.

If you have lost the card, write to the above address giving the relevant information about your departure from the US. See www.usembassy.org.uk for further information.

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