Is there a quick way to do this? My rear brake is sticking but could it be the brake line and not the caliper? Is there a way to tell?

Can't see how a brake line would cause this and the callipers are prone to piston seizure. 2012 TDV8 Vogue (L322)

Flexible brake lines can cause the same symptoms as a binding brake caliper if they develop a split or pinhole on the inside surface, it's more common than you'd think.
The way to check is to crack off the caliper bleed nipple, if there is any residual back pressure, it will be vented and the brake will release, if it's a seized / sticking brake caliper piston or slides, there will be no change in drag.

Much appreciated Phoenix!

No worries! Don't forget to purge any air that might have entered the system, get someone to pump the brake pedal a few times and hold down, then crack off the bleed nipple 'a bit' whilst they keep pressure on the brake.