The prohibition on transport means you can't take it to the range to shoot.
And where did it say the locked-to-the-car requirement applied only to handguns?
Why would the transportation of long guns in this fashion even be problematic? What are you upset Brits can't carry their long guns into the mall or something?
I have no problem with a carry-it-in-the-boot law. I have a problem with the lock-it-to-the-car law.