This manoeuvre, like other Terpsichorean arts, must be executed with the right steps, in the right order.
1) Declare yourself dissatisfied with the direction that your party has taken. It has forgotten the ideals of its founders, and followed the devices and desires of the new leaders’ hearts.
2) Denounce the current leaders for the futility of their present courses. Ascribe the direction of these to their tender years.
3) Cry aloud that your party is leaving you, not that you are leaving it.
4) Park yourself on a convenient hillock, gazing wistfully into the middle distance. Declare your deep concern for your country. (N.B. Do not remind it how often you have saved it: you wouldn’t want to end up like Cicero.)
5) Wait for representatives of your next party to approach the foot of your hillock. Permit them to engage you in conversation. Declare loudly enough for everybody to hear how delighted you are to find how much their principle are those to which you have always adhered.
6) Descend from the clouds at their next conferences, indicating clearly (but not blatantly obviously) the policy area in which you are most interested.
7) Accept the relevant portfolio.
8) Carry on as if this was the party to which youd had always belonged.