Every winter in England there are reports of the "winter vomiting bug" aka norovirus, and people have a fair (double digits) chance of getting it. From memory over the last ten years I've caught that unpleasant virus a handful of times.
It is easily spread by sick people touching things (eg handle bars in the tube) which you then touch, before touching something that goes into your mouth. If Ebola came to the uk without major changes in behaviour it would likely infect millions of active, young people via London.
The last flu epidemic with a major death toll was the pandemic of 1918, which is estimated to have killed more people than World War I. A less deadly version of the same strain was officially listed as an epidemic in 2009.