According to Official Guinness Records,
The fastest marathon in police uniform was 3 hr 09 min 52 sec by Paul Swan (UK) at the 2011 Virgin London Marathon in London, UK, on 17 April 2011.
Swann was required to wear helmet/cap, belt, shirt and trousers. He also wore a vest with other police materials such as flashlights and handcuffs.
For a complete list of 2011 records, please visit 2011 Guinness Records in United Kingdom.