The guarantee is the principal selling point of the 'Best 90' account. Many investors will probably be unaware that it is not permanent, let alone that it could disappear in fewer than three months.
A C & G spokesman said the society would be writing to account holders in due course to let them know what had been decided. However, no date has been set for sending the letters.
All the C & G can confirm is that if the guarantee is withdrawn, the account will become an instant access, no-penalty account from 1 May.
Investors could then take out their money immediately and run into the arms of any higher-paying building society. C & G investors should make a note in their diaries now for 1 May to remind them that some action may be needed.
If C & G does decide to keep the guarantee going and an investors want to close the account, then the 90-day notice period or penalty stands.
According to the C & G spokesman, some investors have already given notice 'just in case the guarantee does run on'.
This could be sound advice, but there may be a catch. The Best 90 account has been closed to new investors since April last year.
If account holders decide to give notice to close the arrangement, and then have a change of heart, they may not be able to get back in. They need to check with the C & G before taking any action.