£1 Noter British Armed Forces Special Vouchers (BAFSVs)

3 British military issue £1 notes.

These are British Armed Forces Special Vouchers (BAFSVs), known to collectors as BAFs. the top two are 2nd Series (you can see “2ND SERIES” printed below “ONE POUND” on the front), and only the bottom green/maroon note is 4th Series. 
What they were for
These were issued from 1946 onwards as a parallel currency for British servicemen stationed overseas. The purpose was twofold: to stop sterling leaking into local economies and being traded on black markets, and to control what troops could spend where. As the reverse states, they were valid only for transactions within official NAAFI canteens and organisations laid down in General Routine Orders of the theatre. Civilians and non-British service personnel weren’t entitled to use them, and improper use was a disciplinary offence. They didn’t entitle the bearer to anything off-base — purely a closed-loop military currency.
The two series you have
2nd Series (the top two, AA prefix): Issued 1948, withdrawn 1948 after a short run. Printed by Thomas De La Rue.
4th Series (the bottom, K/1 prefix): Issued 1962, used during the Cold War period in places like BAOR Germany, Cyprus, and other British garrisons.