Psychological experiments have shown how people can be conditioned by numbers. In one experiment people were asked to write down the last two digits from their social security number. They were then asked to submit bids for wine and chocolate. When the bidders were ranked by social security number, the half with bigger numbers placed bids that were between 60% and 120% more than the others! The idea is that we are subconsciously conditioned. This is called the adjustment heuristic.
It's not just the average "Joe" who falls foul of this trick. This link describes how demands for severe sentences have been shown to skew the actual sentences handed down by experienced judges.
During Parliamentary debates our politicians hear the same discussion and view the same evidence. This could, conceivably, make them more susceptible to the adjustment heuristic. However, if voters decide based on information from a wide range of different sources - from more information than any one person could review - they may, as a group, be less susceptible to this type of conditioning.