Its not obligitory to have a air bag but as far as the future implications. Obviously if the air bag has been deployed this will throw up a fault on the system. the below extract may help.
On 1 January 2012, new rules were added to the current MOT by the Department for Transport (DfT) to comply with European testing procedures.
It's a pretty substantial list, but there's one which could mean big bills for thousands of drivers. If your car has any illuminated warning lamps, whether it is the airbag, seatbelt, ESP, SRS, ABS or others, it will soon fail the MOT.
It's not all bad news. If your car's MOT runs out before the 31 March 2012 and you have a warning light that needs addressing, the testers will treat it as an 'advisory', i.e. advice on what needs to be done for the next MOT.
However, if your MOT is due after 1 April 2012, you better get your skates on and get the warning light (or other faults in the list below) fixed, otherwise you'll receive the dreaded fail sheet.
The AA has kindly published a summary of the new rules. If you think your car needs attention on any of the points below but still has a long MOT left, we recommend getting it seen to sooner rather than later.