If your GP refers you to the consultant for any medical treatment, every appointment you attend a briefing of your appointment which contains any tests carried, any changes to your medication or treatment regime is all included in this letter!
If you are under a consultant is over-seeing your treatment then your GP can't change aspects such as medication or dose without first seeking the advice of the GP, unless an emergency situation is involved!
You can ask your consultant to be copied in on any communications that he/she sends to your GP!
The only various within communications is based on what computer set up they've got, some area's the hospital and surgery records are linked, so both hospital and GP can view both records, other such as my area the we have completely two different computer systems... My GP can access my hospital records, and my consultant can't access my GP records.. So letters are sent to and from, filling each other in on my results etc!
I have my bloods done around a fortnight before I attend the hospital clinic, and if I don't want to what for my consultant to tell me the results I can phone my GP for them, then fortnight to 3 weeks later I receive the letter from my consultant detailing all my test results, and briefing on my appointment out come..