Note that section 2 (1) (b) appears to answer those questions which have arisen in relation to people employed in the public service but who do not have pension entitlements. It looks as though such a person is not liable for the levy unless they receive a payment is lieu of membership [in a public service pension scheme].
Section 7 (2) also confirms that the levy does not count towards the deduction limits as a percentage of income for pension contributions ("[...] is not a contribution for the purposes of the Pensions Act 1990").
Tax deductibility of levy also confirmed. It also provides for reductions in pay of certain classes who are not directly paid in public service, including health professionals (section 9), and others (section 10). In my lay reading of this, this allows reductions in pay commensurate with the effect of the levy for people who are not directly in the employ of the state but whose pay effectively originates from the Exchequer.