Breaking a timing chain must be a pretty rare event. I know timing belts go but I have never heard of a chain snapping. I wonder if something else seized and caused it to break? Have they been able to tell you, or is that one of those 'let us take it to bits first' type questions?
Is there any way you can look into the bores and see if there's any damage? Multi-valve engines do have a higher risk of valve strike but I don't know what the clearance is on the 4.4. Try ringing either BMW UK or another dealer if no one here knows.
How many miles had you done? Whatever the case you have my sympathy!! There might be an independent dealer who can take it on and they charge a lot less per hour. I have just had a look in the UK BMW Car Club Magazine and the only independent listed who might help is a long way off in Milton Keynes - PCS. Might be worth giving them a call.
PCS - BMW index
(By the way, does the terms RA 5 mean anything to you?)
Rick