All 3 colours of uniform have generally got around it to date by saying something along the lines of 'you are encouraged to pursue progress to CEng, IEng etc' and, therefore, it was not a 'must' and they did not have to pay for it - to not have it and being a 'must' then you would not, perhaps, have been able to fulfill your role.
HC appears to have changed that. In reality CEng is not that hard to achieve and the professional bodies, as charities, will want your yearly subscriptions.
Is it wise for the afterlife?
Possibly, BS baffles brains etc. Some roles in civ div demand it in the same way they demand Prince 2 - no one uses Prince 2.
Can SLC be used for the subscription?
No - SLC can be used for the assessment phase but nothing else.
G
CEng