I think it is an usage specific to the UK.

Use of a plural verb after a singular noun denoting a group of persons (known as a noun of multitude) is commoner in the U.K. than in the U.S. Fowler wrote: "The Cabinet is divided is better, because in the order of thought a whole must precede division; and The Cabinet are agreed is better, because it takes two or more to agree."

Taken from: http://alt-usage-english.org/groupnames.html