Here you go, printed from the government site this morning. This is the actual law as worded and is quite unequivical. The post it note found on the fridge door of the CPS canteen in 1997 is useful, but contrary to the letter of the law. I wouldn't risk by ability to keep guns and liberty on it.
One theory is that the wording was supposed to be "up to .22 rimfire" which would at least make sense.

3.2 Section 5(1) of the 1968 Act, as modified by the Transfer of Functions (ProhibitedWeapons) Order 1968 and amended by the 1988 Act, the 1992 Regulations, the 1997Acts, the Scotland Act 1998 (Transfer of Functions to Scottish Ministers etc.) Order 1999,the Anti-social Behaviour Act 2003 and the Anti-social Behaviour, Crime and Policing Act20141, makes it unlawful to purchase, acquire or possess, without the authority of theSecretary of State, any prohibited weapon or ammunition. Section 5(1A) of the 1968 Actmakes it unlawful to purchase, acquire or possess, without the authority of the Secretary ofState, any prohibited weapon or ammunition. Unlike the section 5 (1) offence, the section
5 (2A) offence contained in the Anti-social Behaviour, Crime and Policing Act 2014 coversthe manufacture, sale or transfer of any prohibited weapon or prohibited ammunition andthe possession for sale or transfer and, purchase or acquisition for sale or transfer of anyprohibited weapon or prohibited ammunition.
Those weapons and ammunition, which are prohibited, consist of:





  1. i) any firearm which is so designed or adapted that two or more missiles can besuccessively discharged without repeated pressure on the trigger (section 5(1)(a));


  2. ii) any self-loading or pump-action rifled gun other than one which is chambered for .22rimfire cartridges (section 5(1)(ab));


  3. iii) any firearm which either has a barrel less than 30 centimetres in length or is less than60 centimetres in length overall, other than an air weapon, a muzzle-loading gun or afirearm designed as signalling apparatus (section 5(1)(aba));


  4. iv) any self-loading or pump-action smooth-bore gun which is not an air weapon orchambered for .22 rimfire cartridges and either has a barrel less than 24 inches inlength or is less than 40 inches in length overall (section 5(1)(ac));


  5. v) any smooth-bore revolver gun other than one which is chambered for 9mm rimfirecartridges or a muzzle-loading revolver gun (section 5(1)(ad));