There are two rule books I am looking at first is Part P this is freely available to all see
http://www.planningportal.gov.uk/england/professionals/en/4000000001253.html the second is BS7671:2008 which costs £65 but the part you require is available as free down load at
http://www.theiet.org/publishing/wiring-regulations/forms/index.cfm
As I see it the problem in forcing anyone to give the Minor works cert FOC is to show they must issue it.
The Part P document says you must follow BS7671 but also states 1.13 that it is not required.
But on page 15 of the forms it says:
GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (The IEE Wiring Regulations).
You should have received an original Certificate and the contractor should have retained a duplicate Certificate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it, immediately to the owner.
A separate Certificate should have been received for each existing circuit on which minor works have been carried out. This Certificate is not appropriate if you requested the contractor to undertake more extensive installation work, for which you should have received an Electrical Installation Certificate.
The "original" Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the minor electrical installation work carried out complied with the requirements of British Standard 7671 at the time the Certificate was issued.
I would say that leaves little room for manoeuvre and to me the original should be given to you.
If he has filled one in then I can't see how he can hang onto it. I wait to see what the others on here say.
Eric