The term ‘Maximum’ applies to old-style investment-linked contracts. These disappeared post-RDR with the introduction of fees for investment products.
‘Maximum’ means that you pay the minimum premium for the maximum amount of cover. Because the contract was investment-linked, if investments performed well then your premium levels could be maintained but the likelihood was that when it came to a review point, then your premiums would go up, significantly.
Premiums now on guaranteed WoL products are normally ‘level’ like on a term assurance contract.