If you click on the VOSA link from the web site above and look at the statement for testing air bag lights compared to ABS lights they are different. ABS states the light must illuminate and there is a failure for non illumination. Where as for air bag lights it sayes check that a fault is not indicated. There is no option for failure for non illumination
http://www.dft.gov.uk/vosa/repository/SN%2001%202013%20V1.0.pdf Annex A: Page 3:
"SRS components including airbags, seat belt pre-tensioners, seat belt load limiters and SRS malfunction indicator lamp"
http://www.theplace.pwp.blueyonder.co.uk/m4_int.pdf Go to section 5.4 page 1. (this is the April 2013 version)
It states
Method of Inspection
1. As far as practicable, check that all airbags fitted as original equipment are present and not obviously defective.
2. Check that the Supplementary Restraint 2. System (SRS) malfunction indicator lamp (MIL) does not indicate a fault in the system.
Reason for Rejection
This inspection applies to airbags, seat belt pretensioners and seat belt load limiters fitted as original equipment other than on Class 3 vehicles.
1. An airbag obviously missing or defective (Note: A passenger airbag that has been switched off is not a Reason for Rejection.)
2. A Supplementary Restraint System (SRS) malfunction indicator lamp indicating a system malfunction.
So I think that will come down to your Garage/MOT tester, however should anyone have an accident and it then turned out the vehicle was originally fitted with an airbag (which has been removed) , then expect fun and games with insurers. So best to advise them then