Why do you think Labour would listen to a letter when:
Most of us have already written letters.
They have a moderate GC voice in the party(Duffield) and rather than listen or at least entertain different views, they shut it down by bullying behaviour.
Labour are on record responding to your position, just not the response you want to hear. Cervix unmentionable, rights hoarding dinosaurs.
What exactly do you think you/we will say in these letters that will make them change course? They have access to crime stats, they have access to educational stats and mental health stats. They have far more resources than you or I, and have been pointed in the right direction numerous times.
Just accept the fact that they don't allign with you. You won't explode if you vote for the Tories once or spoil your vote.