"After the horse has bolted" definitely the best time to shut stable door, confirms Labour MP

Labour’s real battle over Brexit starts ‘after article 50 is triggered’ Emily Thornberry says Brexit bill must be voted through and party should focus on shaping Britain’s future outside the EU

Sound advice. I always find that the best way to deal with any serious problem is to wait until the problem starts having a catastrophic effect on my life and make sure that I've personally taken action to ensure that the problem has become irreversible. You need to pick your battles and, as everybody knows, losing battles are the only ones worth fighting.