Here's a quote from the MKA Ecology website, I'm pretty sure this is the current legal status.
All six terrestrial British reptile species are protected by the Wildlife and Countryside Act 1981, as amended. The level of protection however depends upon the species. The common lizard, slow worm, adder and grass snake are all partly protected so that it is an offence to kill, injure, or sell these animals. The smooth snake and sand lizard, Britains rarest reptiles, are fully protected thus also making it an offence to take or possess, intentionally or recklessly to disturb or destroy an occupied place of shelter. In addition, the Sand Lizard, and Smooth Snake are also given protection under the Habitats Directive (1994), where they are listed as European protected species in Schedule 2. Sand Lizards are also designated a specific UK Biodiversity Action Plan(UK BAP), ( a government response to the Rio summit (1992) where member states are committed to applying Species Action Plans.)(
www.ukbap.org.uk.)
So, you can 'disturb', take or posses Adders as much as you like.... but you can't sell 'em!