Yes, within reason, however, over here in Oz, Ive heard that they are set about 3 to 5% above but as 'durbar' has said, various things come into play.
If you've fitted slightly larger sports wheels, they can affect your actual speed reading compared to your speedometer.
Example - My daughter fitted 20inch mags & wheels to her Suzuki Swift, which came standard with something like 15 inch, so there is a big difference
which will no doubt give a wrong reading on the speedo.
If your motor came standard with say, a 1.2 size engine ............... and now you've fitted a turbo or a larger engine, the calibration will be out.
Summary - I'd be inclined to trust the car reading over a after market product.
Cheers,
Aussie