"I have received several election leaflets and letters directly addressed to me and recently I had some bloke from the Labour party phoning me (and it wasn't even an election going on either!). I checked electoral law and contacted the electoral commission but the law is really woolly. It says that election candidates can have a copy of the electoral register and use it for electoral purposes. But it doesn't explicitly state what those purposes are. I would argue that using my personal details to send me letters and then using my phone number to phone me especially when its not actually during an election is in clear breach of the law."
Political junk mail addressed to you can be stopped in the same way as any other type of addressed junk mail. If you're registered with the Mailing Preference Service you shouldn't get addressed mailings from Labour, the Tories, and the Lib Dems; the opt-out scheme should prevent addressed junk mail from members of the Direct Marketing Association, and the three main parties are all members of the association. To my knowledge no other political parties are members of the Direct Marketing Association, and so other parties won't check to see if you're registered with the Mailing Preference Service.
Any addressed junk mail can be stopped by sending the sender a data protection notice. This is a demand, made with reference to the Data Protection Act 1998, to stop (or not begin) processing your personal details for 'direct marketing' purposes. Data protection notices are legally binding, and apply to any type of 'direct marketing' - including direct mail campaigns undertaken by charities and political parties. For more information and an example notice letter, see the Contact senders page in the Guide.
You might find that your local Labour Party / Tories / Lib Dems doesn't bother checking if you're registered with the Mailing Preference Service or have sent the party a data protection notice. If so, they're breaching either the Direct Marketing Association's code of practice and/or the Data Protection Act 1998. The fact that they're allowed to use the full version of the electoral register as a cheap and convenient mailing list doesn't allow them to contact everybody on the full register.
As for the unsolicited phone calls, I'm not an expert in this field. I'm registered with the Telephone Preference Service but do get the occasional call from the Labour Party myself. I did once tell them they shouldn't be contacting people registered with this opt-out scheme; the caller's reply was that my registration with the Telephone Preference Service was irrelevant because they were not making sales calls. You might want to contact the Information Commissioner's Office the exact rules for unsolicited calls from political parties; they got a very helpful helpline: 0303 123 1113.
Finally, if you're not registered with the Mailing and Telephone Preference Service, you can sign up to both at the same time at stayprivate.org.