Be aware of the introduction of any automated systems allowing you to book interline tickets. Earlier this year BA introduced such a system stating that it would be far better for the staff and easier to book interline tickets. ( It is ... if you know that you need a back-up ticket at least 7 days before departure as the tickets have to be posted and cannot be collected ).
They have now announced that there will be a USD3 NON_REFUNDABLE charge on each sector made using the system ... thats USD3 per person per sector or about 10% on the cost for a ZM1 ticket.
Then don't use the system, book by phone, I hear you say .... unfortunately we now have no option but to use it.
Other carriers beware !!!!