Cloned my system disc to brand new drive. On restart, the original source disc is still marked as bootable, not the new target disc. Tried three times with same result. Cloned Job completes successfully with no error messages.

As per instructions, did clone both the C volume and the 100mb system reserved .

Any help much appreciated.

Have you run Fixboot which is on the Reflect Rescue CD/USB key?
Make sure you select the Windows on the correct device or better still just have the new clone connected.

Thanks, not yet. I read about that after I posted. I guess I should have read it first 😊

Removed all drives except the new one created by the cloning process. It started right up without a problem without needing to use the rescued disc.
I am guessing that Win got confused with two discs marked as boot and used the first one it found. Anyway all fixed.

This is one of those things that used to be mandatory in older versions of Windows as in the IDE disk era - disconnect other OS drives until the first boot. I had thought it didn't matter anymore but given various things I've seen, I'd say it is still a problem where the best thing to do is to disconnect the original drive until the first boot. Then it can be reconnected.