This question already has an answer here:
Should I use "is increasing" or "are increasing" in this sentence:
Second, the frequency of attacks and number of deaths is increasing.
The original post uses "is". Is it British English?
SOURCE FinancialTimes The ‘war on terror’ is going backwards By Gideon Rachman January 19 2015 http://webcache.googleusercontent.com/search?q=cache:zNx0ufCLzAwJ:www.ft.com/cms/s/0/98cf268c-9fd2-11e4-aa89-00144feab7de.html+&cd=1&hl=en&ct=clnk&gl=kr&client=safari