NCT

Are you meant to bring your car to a garage before your NCT to see if there's anything wrong with it or do you bring it for the NCT and then fix what needs to be fixed and resit the NCT?

Say if you brought it to the garage before would they check it for everything the way they would in the NCT or would they just check for what are the most popular reasons for failure? Because if that's the case wouldn't you be better to get the NCT first to see what's wrong if they do a more detail inspection?

I have a Lexus GS 300 (95 reg) with an airbag light always on. Does this mean it well fail its next NCT test? Thanks

If a car is clocked between NCT tests will it fail? As in, if it shows up this year with less mileage than it did at the last test, will it be noticed?

I have a 2007 Opel Corsa. I know I need to get the NCT done this year, but I don't know when it is due or anything.  Friends of mine are saying that they write out to you and let you know; others are saying that you need to ring up. My question is, does the NCT company write to customers who are due an NCT?