The data upload is due to commence in March 2014, and all householders should receive a leaflet 'Better Information Means Better Care' through their letterbox in January, although it will not be addressed, and you could have already disposed of it as 'junk mail'.
There are implications to allowing this information to be shared by your doctor, who cannot object - but you can. My suggestion would be to follow the above link, and make sure you fully understand what is about to happen with your personal data, and should you wish to opt out, then here is a link to obtain the form above.
There is no need to contact or make a special appointment with you GP about this, should you wish to do so, simply fill out the form and hand it in to your surgery.
The link to the above form is: http://medconfidential.org/wp-content/uploads/2014/01/caredata_trifold.pdf
For the 'official' take on this read here: http://www.nhs.uk/NHSEngland/thenhs/records/healthrecords/Pages/care-data.aspx
*Update. I have just received a call from my own GP's surgery after I used the above form sent by fax to them, and after all the official documentation I have read today stating that there is no need to visit and that a generic form may be used, they have insisted that we use their own form to complete this request - handed to them in person. Bureaucracy gone mad!