One from Falkvinge (first hit on google), responding about as you'd expect [1], and a link to the actual law [2]. It doesn't make encryption illegal, it just makes it illegal to not produce the key on demand. You can decide which is worse.

1. http://falkvinge.net/2012/07/12/in-the-uk-you-will-go-to-jai...

2. http://www.legislation.gov.uk/ukpga/2000/23/section/53