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Last time I was there - maybe a year ago - it was possible to walk along the perimeter road to Hatton Cross - note, verge, not footpath..
True: if you want to avoid the verge (and I’d recommend you do so because the southern perimeter road is v busy and that verge is narrow) the trick is to transition off the perimeter road footpath and take the footpath which runs along the north side of the adjacent and parallel A30. You can do that by going through a cunningly positioned opening in a fence that divides the two roads about 100 metres or so east of the T4 Premier Inn...adds about a metre or two to your walking distance to Hatton X.
Still hopeful of checking out the first bit of this legendary walk after cease work tonight.....
edit it to add: Skipness 1 E is correct, it can be done...for the benefit of the OP.
Turn left leaving arrivals.
head past all the bustops, at the far end you have to turn right, through a bike/motorbike parking area.
At the end of that exit to the left and pick up the footpath opposite that runs under the walkway to the Hilton/Prem Inn. Follow that for 100 metres - You’ll find yourself on the southern perimeter road.
Good luck...