Diet nannies will spend Christmas telling us ‘you are what you eat’ but in the House of Commons ‘you are where you sit’. Are you a Tory Whips’ stooge or a Dominic Grieve groupie aching to block Brexit, a braw new blue Scot or an English provincial plodder without hope of advancement? Parliament-watchers discern plenty about your political leanings from where you park your posterior.