It would be ludicrous to treat this as deprivation as the promotion of exactly this has led to a veritable deluge and something of a backlog. In thirty seven years I have come across enquiries about a voluntary NI payment once maybe every couple of years. Recently I dealt with about twelve in one day. The campaign is hugely successful albeit that in the majority of cases I have seen no real benefit to the payment. That’s nothing to the point here though.
You will note that said campaign does not add the caveat that if you’re currently in receipt of means-tested benefits or just outside of that there is a risk of deprivation being activated. The issue is not whether you have done something sensible or not. It’s whether part of your reasoning was to gain benefit or an increase in benefit. Very difficult to make it stick as the starting point is that the claimant knew the capital limits and the onus to show that falls on the party seeking to change the decision.
“We sent them a leaflet” or “They must have known” rarely cut the mustard nowadays. You also have someone already under the upper capital limit. Were they to challenge any attempt to argue deprivation tribunals tend to take a dim view of such cases. Deprivation to obtain benefit is always worth examination but deprivation to increase is a much bigger ask as it’s fairly easy to refute.