Tyre tread depth not good on outside of tyre...

2 quick questions:-
NCT due soon and about 1 1/2" of the outside of each of the front tyres (17X200X40) is badly worn (issue has been sorted). The rest of the tyre has a good tread.

1. Is this safe?
2. In order to pass the NCT does the entire tyre have to pass the tread depth test?

Page 61 (38) : [broken link removed]


States:

TYRE TREAD
Method of Testing
Check with a tyre tread depth gauge, that the central three-quarters of the tread pattern has a depth of at least 1.6
millimetres around the full circumference of the tyre.
NOTES:
(a) It will not always be possible to see the complete tyre from ground level, especially on twin wheels and on vehicles
where the body shrouds part of the tyres. In such cases the the examination should be completed from a position
under the vehicle with the wheel in the raised position.
(b) Where the pattern is interrupted by tread wear indicators but has at least 1.6 mm overall tread depth the tyre
concerned should not be failed for inadequate tread-depth.
(c) The tread pattern means the combination of plain surfaces and groves extending across the breath of the tread but
excludes any tread wear indicators or features which are designed to wear out substantially before the rest of the
pattern under normal conditions of use.
Depth of Tread Depth of less than 1.6 mm in the central three-quarters of the tread
pattern.

Towger- Thanks for the comprehensive answer.