I have also heard the term "strep" in both the US and the UK, but Marlespo's quote above reminds me that some English people seem to call any cold "the flu". Influenza is a much more serious - possibly fatal - disease.
They do!
Our students will come in all winter saying, 'I have flu'. One of the academics always quips, 'If you really had flu, you wouldn't be walking in here gabbing on your mobile moaning about how ill you are.'
Having had influenza a few times in my life, there isn't a cold around that can compare. Damn, that is ill! Last time, I wound up spending Xmas in hospital w/pneumonia. It SUCKED!
The £20 note test is the way to qualify it. If there's a £20 note lying 10 feet in front of you and you're too ill, feverish and weak to go get it, you have flu.