If the seats are of a tipping variety, the tipping mechanism must be secure and adequately strong. Brakes may be checked, in so far as testing the feel of the brake pedal. The suspension and steering may also be checked for play. It used to be a requirement to carry one of these. This regulation is no longer in force, but it is a good idea to have one, and will keep the scrutineer happy.
Most vehicles have such a mechanism as standard.
Any items carried in the car must be securely fastened down, such that in the event of an accident things can not fly around the car and hit some one. The spare wheel and battery will both be checked for security. All cars must have a current MOT - take it with you to the event just in case some one asks to see it. The above is not guaranteed to be exhaustive, and most scrutineers have their own idiosyncrasies. However, if your car conforms to the above and appears generally road worthy then you should have no problems.