Not against the offence itself - "you are guilty" by terms of Strict Liablity. However, you might be able to appeal to get a lighter sentence [ lower points / fine in this case] if the judge concludes there is enough mitigating circumstances. Having an incorrect speedo - whether that is the truth or not, it is no defence againt the actual charge.

Ask the guys here if you want more advice...

http://www.5ive-o.com/web/viewforum.php?f=4 (Courtesy of Doug Stirling )