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 - for example by tackling 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. Read guidance from the Crown Prosecution Service (PDF, 136KB).
You do not have to wait to be attacked before defending yourself in your home.
However, you could be prosecuted if, for example, you:
carry on attacking the intruder even if you’re no longer in danger
pre-plan a trap for someone - rather than involve the police