Currency specialist Caxton FX is offering both new and existing customers a free buy back guarantee for their holiday money for the month of August.

It promises to buy back your unused currency at the same rate you bought it for, so if the exchange rate changes you won’t lose out.

The offer is available for those loading £500 or more worth of currency onto a Caxton prepaid currency card, and it will be available until midnight on 31 August.

Caxton’s buy back guarantee launched in June and it usually costs £4.99 for each currency, so if for example you were due to visit the US and Europe, it would cost you £9.98.

It is valid for 90 days from the day of purchase, or 30 days from your first overseas transaction or ATM withdrawal, whichever’s first. There is no redemption fee for changing your money back to sterling.

As you have to be a Caxton FX customer and you’re buying currency from it, the guarantee doesn’t apply to currency bought from other bureaux.

However, it told us that its rates are “very competitive versus banks and airports on travel money” – you can use its comparison tool to see how much you can get on average versus other exchange firms.