A public spending watchdog examines the property arrangements of royals including Andrew Mountbatten-Windsor.
The Greater Manchester mayor would need to win the by-election in Makerfield to be a possible candidate.
The shift marks a significant rise over the last five years, but experts say there is no single, clear explanation for the increase.
The charity says it is facing "an exceptionally challenging trading environment".
Tributes are paid to Lt Cdr Chris Gayson, 42, Lt Lily-Mae Fisher, 31, and Petty Officer Owen Green, 24.