Never seen uncancelled, these were "receipts" for deposits on account to Post Office Savings Accounts, eventually withdrawn in 1930 and superceded by National Savings stamps.
Post Office Savings Bank
Deposit Book 1912
(01) 1/- Blue & Red (1912)
Market Value : £85.00
Deposit Book 1920
1/- Blue & Red-Brown (1920)
Market Value : £65.00