VH-RMD that little piece of vital information (EK flight number) should make me reverse my previous answer since the flight is not operated AND marketed by an OW member. However I have some hope that you will be able to persuade the Al Safwa staff to do so especially if your ticket has a QF flight number.
Good luck, and let us know how it goes.

Just to follow up;

The delightful agents at the Al Safwa desk at HIA were happy to tag my luggage through to LGW (QR-EK) but no boarding pass.

The delightful agents at First Class desk in LHR were happy to tag my luggage through to DOH (EK-QR) with boarding passes.

These were two tickets on separate PNR.

The tickets were both award tickets and the EK ticket was obtained using QF points but with EK flight numbers.

VH-RMD thanks for the follow up. I am sure that you are pleased with the result. I was expecting that Al Safwa would interline across airlines but that EK at LHR did the same was an unexpected bonus.

Anybody know if Swiss will interline to Qatar?

Today to Heathrow QR would not interline my luggage with PG on a separate PNR because they Re not a Oneworld carrier (but have an interline agreement). They said it was a strict policy based on their responsibility for the luggage, even if PG was the one to lose it.

Hi giblet, this is exactly as per their policy. QR will interline to other OneWorld carriers as an extension and nod to the former OW policy of interlining. Some other OW carriers continue to interline.

But PG (Bangkok Air), although it is an interline partner this only comes into effect on a through journey on a single PNR, not for separate ticketed flights.

Qatar did exactly what their policy said they would do. And they are right, that if your baggage went missing or was damaged as a result of being carried on PG interlined from QR, it is QR that would be liable under the Montreal convention.

Plunet, I'm not complaining, merely relaying my experience. In another thread it was suggested they might be willing to do it, so I thought it would be helpful to make clear to other pax in a similar situation that it's not possible.