Safe Passage has suggested this template for writing to MPs. Obviously, you are free to add your own concerns.
“I am deeply worried by the Home Secretary and Prime Minister’s plan to destroy the right to asylum in the UK with their ‘Illegal Migration Bill’.
If this Bill becomes law, Britain’s proud tradition of welcoming those fleeing persecution will be trashed. This law will mean that any refugee who cannot access one of the few safe routes will be denied the chance to reunite with their family and live safely in the UK. Instead, they would be detained by the Home Secretary before being banished forever with no chance to reach their family here in the UK or establish a new life here. “