We don't yet know why those poor people were in the lorry at all, so it's far to early to call them 'immigrants'. They might be trafficked people. Whatever the reason for them being there, it's a terrible way to die and utterly inhuman of whoever was responsible for sealing them up in the lorry.
Gabriella it might help to remember that for some desperate people - possibly these, but we don't yet know - the UK is indeed Nirvana. We don't live in a war zone; disease and poverty, though they exist, are not the norm. Some people's lives are so unbearable they feel they have little choice, so they risk their lives, hoping for something better. There will always be those who will exploit that fear and desperation and make money out of it - we all know it's widespread. It's unlikely the perpetrators will be caught and even if they were, there are plenty more ready to risk the lives of terrified people or traffic them into slavery.