Never having p.p. vs. Having never p.p.?

Question

Recently I have encountered 'Having not p.p.', which puts not between having and p.p.

In fact, I was taught to put not before having p.p. And BBC Learning English confirms it. Which is the definite grammar rule?

Negative participle clauses are also possible, in which case not normally comes before the -ing form or past participle:

Not having had a shower for two days, I was desperate to get to the bathroom.

BBC Learning English

Answer 1

The BBC guidance describes the most usual form; it does not give a rule. 'Not having done something' and 'Having not done something' are equivalent and there is no 'rule' that says the first is correct and the second incorrect. You can negate the verb phrase (not [having done something]) or the direct object (having not done something).