That's been a nagging worry for a couple of years - so I emailed Citroen UK. Here's their reply which I'll print out and carry with me:- Thank you for your e-mail dated 11 September 2007. I can confirm that there is no legal requirement to mask right-hand drive headlamps for use on the continent. This is due to the Z pattern beam that is created by the xenon headlights, fitted as standard on the Citroën C5 Exclusive models, rather than a standard flat beam on conventional headlights. The only stipulation is that the headlamps do not dazzle oncoming drivers and this applies equally to driving here in the UK as to abroad. In addition, the C5 has Hydractive self-levelling suspension and, therefore, there is not the risk of dazzling usually associated with a heavily laden vehicle. Drivers should have the headlamp adjustment checked before travelling. If still concerned, they could at this time have the height of the headlamp beam set to a lower position. This would reduce the possibility of dazzling even further. It must not be forgotten that any such adjustment would impair the visibility provided by the headlamps at night. Just as with masked headlamps, modifying the headlamp adjustment will reduce the effectiveness and, therefore, driving speeds must always be adapted to take this into account.