Despite the copyright laws, the architect will have a hard job preventing anyone using his drawings if they have been given them by the original owner/whoever paid for the plans.
One thing should be made absolutely clear - it is a common misconception that when you pay an architect to design something that you gain ownership of the drawings. This is false. A client pays for design services, the architect uses drawings to illustrate those design services.
Also, DO NOT presume that just because the drawings of your house are in the public domain that you are free to use them... this is another fallacy. Publishing drawings (or any works) publicly, or displaying them online does NOT relinquish any copyrights (many councils are now displaying caution notes to this effect on their sites).
In short, the architect holds copyright over their drawings and issues them to others. They can choose to give up their copyright for free or for a fee. You should check the drawings to see who the copyright holder is - you should find somewhere the (C) symbol and name. However, if you make any un-authorised changes to the plans, or make any copies of the plans then quite clearly you will have infringed on the owners copyright.
An designer won't be able to PREVENT someone from using their drawings, but they CAN confront infringements of their copyright material and in such cases the person who breached the law will have a hard time fighting such a clear cut claim against them.
The cost of pursuing a copyright case may be high, but it is likely that the party that caused the breach will in the end be forced to pay full costs, and may be additionally required to pay the architect for loss of earnings as well as a fee for the retrospective use of the plans in that instance (ie: if you make a further application using their plans that they could have charged you for).
My advice is as follows:
1.Contact the original architect. Ask them if they can issue you with drawings. They may issue them to you for free (though this does not mean you can copy or adapt them without their permission).
2.If you do want to make changes etc. then ask them if they are able to issue you with the computer drawing file. Not many designers will freely give this up, because it allows anyone to take the original work and then carry on a project. Retaining copyright on this is pretty much impossible because someone else can say they re-measured the building and drew their own design. For that reason, most designers will charge a fee for this. You will need to weigh up if this cost is more or less than the cost for getting someone else in to measure up and draw plans for you.
3.Ask them to provide a quote to continue with further stages of work, for example; to make any amendments to the plans, sort out building control details and help point you to some builders.
