Diagram is CORRECT.
Don't you dare give up Billingham!
Think about it. You can do this
Connect your sinks, blank off what's not used. Look at the U bend and realise you can position it virtually anywhere. You'll need 2 x elbow compression fittings plus some 40mm push fit pipe.
On the end of the pipe coming out of the wall put your elbow. As you look at it the open end will face to about 10 o'clock (so at an angle upwards).
Your trap (ubend) will need a bit of pipe to come out of it pointing at the wall. At the same distance from the back wall as the pipe to outside cut the pipe from the trap. Put the other elbow on. Measure between the two elbows and cut a new piece of pipe. Fit that. Job done.
My (very expensive) consultation fee will follow shortly...