It is very much operated on a trust basis—the word of a whip that they have all of their members present and are able to pass the full number of votes as available to them. The Parliament is always seen very seriously and it probably would be treated as contempt, if a whip did pass votes they were not entitled to. That has happened only once, in my memory, and the party concerned realized that fact before anybody else did, drew the House's attention to it, and actually changed the vote by one as a result.
On May 17th, 2016. See this statement in context.