I have never been to the uk, but here in old Virginia, I routinely run my 451 70-80 MPH up and down I-95. In normal surface traffic, it easily keeps up and usually ahead of the pack. It is what it is, it is not a performance car, but it has more zip and top speed that the law will allow you to use. If you are a timid person, buy a Hummer or something bigger like a F-550 Ford truck.
The Smart is more than reasonably safe and is really fun to drive.