Engaged Motor Mover

Problem is, and Im sorry to stray a little from OP is with jags electronic hand breaks use em or loose em, cost me a couple of bob on me old S type leaving it in park constantly..

 People said the same of the normal hand brake of my previous cars but once a year at MOT must've been enough .... I'll let you know if my ML electric parking brake breaks due to lack of use. 😉

The problem with "park" is that it is implemented by a very small pawl in the gearbox. It is really just to "park" the gearbox, but it can actually hold the vehicle. Should a vehicle in "park" with the park brake not engaged get even a small dunt from another vehicle, the pawl can give way leaving it free to roll wherever.

So, park brake on public streets or anywhere on a slope.

[Why call it a "hand" brake when most are operated electrically now from a finger swithch?]

Extract from M Class handbook-

Always secure the vehicle correctly against rolling away. Otherwise, the vehicle or its drivetrain could be damaged.
To ensure that the vehicle is secured against rolling away unintentionally:
the electric parking brake must be applied. 

it might if it were a manual gearbox but it is auto,even then I would have expected it to release by driving forward and backward but it has not...so wheels off !A caravan braking system is different as the system is designed to collapse when reversing which will usually free off seized brakes.My advice would always be....do not store a vehicle for weeks on end with the brake applied unless it is on a public road.(during my working life I spent 25 plus years working on motor vehicles and 17 years on touring caravans so I feel well qualified)

Thank you very much for time & effort in finding that for me. 👍 But I do have a manual for my car ..... though I'm still on the sat-nav pages ... 🙄

If one needs to read a book to find out how something works, then it is badly designed and not intuitive. It's bad enough having to look up how to load the CD.

[Why call it a "hand" brake when most are operated electrically now from a finger swithch?]

Mine is operated by my left foot.

Isn't there a film about how to do that? 

The R Class was applied by foot but the release was a pull handle on the dash.

I just see these electrically operated parking brakes as unnecessary complexity.