should one even use fists to deter an intruder in one's home, one will be arrested. One must retreat, retreat, retreat, and call for the bobbies.
That's not correct as well. You can use proportional force that can include lethal force.
Quote GOV.UK.
Householders and the use of force against intruders
Joint Public Statement from the Crown Prosecution Service and the Association of Chief Police Officers.
You can use reasonable force to protect yourself or others if a crime is taking place inside your home.
This means you can:
protect yourself ‘in the heat of the moment’ - this includes using an object as a weapon
stop an intruder running off - eg tackle them to the ground
There’s no specific definition of ‘reasonable force’ - it depends on the circumstances. If you only did what you honestly thought was necessary at the time, this would provide strong evidence that you acted within the law.
Do I have to wait to be attacked?
No, not if you are in your own home and in fear for yourself or others. In those circumstances the law does not require you to wait to be attacked before using defensive force yourself.
If you have acted in reasonable self-defence, as described above, and the intruder dies you will still have acted lawfully. Indeed, there are several such cases where the householder has not been prosecuted. However, if, for example:
having knocked someone unconscious, you then decided to further hurt or kill them to punish them; or
you knew of an intended intruder and set a trap to hurt or to kill them rather than involve the police,
you would be acting with very excessive and gratuitous force and could be prosecuted.
guidance from the Crown Prosecution Service.