"critically evaluate whether the trust enforced in Re Denley's trust deeds (1969) was a purpose trust or a trust in favor of a group of beneficiaries"
To begin with it is neither a pure purpose trust or Trust having direct beneficiaries.
Re Denley says:
The trust will be valid, though expressed to be for a purpose, the trust was directly for the benefit of indirect beneficiaries who can enforce the trust.
It will be void if the benefit is so indirect or intangible or which is so framed as not to give those persons any locus standi to apply to the court to enforce the trust.