According to Official Guinness Records,
The fastest speed achieved by a milk float is 136.081 km/h (84.556 mph) and was created by Weetabix On the Go Breakfast Drinks and driven by Rob Gill (both UK) at Bruntingthorpe, Leicestershire on 25 June 2014.
For a complete list of 2014 records, please visit 2014 Guinness Records in United Kingdom.