In the forum, there is a discussion about singular and plural, and asks whether 'two thirds of the cake' should be followed by a singular or a plural verb. The logic seems unarguable:
Part of the cake has been eaten.
Some of the cake has been eaten.
Most of the cake has been eaten.
Two thirds of the cake has been eaten.
However, I feel that British usage does not reflect this pattern. In BE, we often use the plural in such sentences and wouldn't consider it wrong.
To test this, I went to Google and chose the Language Tools option:
I then did a search for 'two thirds' followed by a singular and a plural verb in the UK and got the following results:
"Two thirds is"- UK pages only 530
"Two thirds are"- UK pages only 1,1720
"One fifth is"- 63
"One fifth are"- 199
It does seem from a quick glance at Google UK pages only that we do use both forms in BE. Google can be used to check rules of usage quickly and does allow us to access examples of usage. It can be a useful sounding board to bounce ideas off. Using the Language Tools option is a good way to focus a search.