(the double zero is dropped for ease)
No, it's 129.40 to clarify that you have not abbreviated 129.25, or 129.50 or 129.75 etc to a single figure.
Amateur radios in the UK have the transmit disabled on airband frequencies. I don't have a scanner but do have two radios for use on the amateur bands and one as a spare for use in an aircraft - this latter can be used to transmit on the airband frequencies. I also have my CAA licence as well as my amateur ones.