driving it home last night an airbag light started flashing on the dashboard and now stays lit the whole time. Is this due to the non standard steering wheel??

yep it is telling you there is a problem with it, there should be an airbag swtch somewhere on the dash normally near the passenger side

Yes!

The switch is for the passengers airbag only! You cannot turn off the drivers, it will fail a MOT like this and the only way to sort is to disconnect the switch/light.

l have changed the seats in my personaly owned work car (vauxhall vectra) the original seats had airbags and the replacements do not. The airbag light is on all the time but it has passed two MOT is like it just explain the reason the light is on.

Yes it is, as the airbag has been disconnected, the ecu sees this & puts the light on to warn u of a problem in the system. As it it at the moment the entire system will be in fail safe mode, even though ur seat belt pretensioners & passenger airbag r connected, they wo not work in a crash. A main dealer may be able to reprogramme the ecu as not having a driver is airbag & set it so the car only has the passenger one & pretensioners (and side airbags if these r present) but i'm not sure if this can be done. At least if u do it this way & it works the other components will work in a crash. If this wo not work the best bet is to remove the bulb from the dash, cover the light with some black tape, or the safest option is fit the original steering wheel & airbag back on.