The best advice I can offer is for you to ring the DWP office that sent you form BF5 04/11 and ask them.
To the best of my knowledge, IB claimants are allowed to holiday in Europe as long as they inform the DWP where they'll be staying.
Perhaps another moderator or member can give you a more definitive answer, as ESA is not a benefit I deal with. When I was a WRO it was IB.
PLEASE READ THE SPOTLIGHTS AREA OF THE FORUM REGULARLY, OTHERWISE YOU MAY MISS OUT ON IMPORTANT INFORMATION. Nothing on this board constitutes legal advice - always consult a professional about specific problems