I have planning permission for a 2 storey extension for which I did the drawings. Do I need to get an architect to do the building regulations drawings? and do I need an architect to sign the extension off?
Get the building work approved under the building notice method, don't bother with an architect it would be a waste of money, find yourself an architectural technician if you want help with the building control issues.
If you have full planning permission, you do not need to submit further plans to building control.
You only need to notify them that work is about to start, (usually 3 days notice), as they will find the plans, and they will want to inspect at various stages, (footings, oversite, insulation,etc), but they will tell you what they want to see, and usually if notified before 10.00am, will do a same day inspection.
I have always found them very helpful, particularly if you ask them how they want you to do something, rather than tell them how you are going to do it. After all, they are the ones with the technical knowledge, and the power to sign the building off