Airbag systems are very complicated.You can't guess at what is at fault.You will need some diagnostic equipt plugged in to establish what is flagged as a problem.

There has been no reason for this light to come on, no sudden braking etc.

errr! why is it on then? The ECU thinks there is a problem somewhere!!

You'll need to get the codes read to establish where the problem is originating. Connections are often the biggest problem, especially to the front seats. You could try checking all connection points first - if you eliminate the fault the light will clear.

On my car the airbag warning was also accompanied by some steering wheel buttons not working - it turned out to be the rotary coupler breaking down.