Not true... the laws on home self-defence have been emphasised more in the last few years, Blair himself even went on TV to say that if someone enters your home you can do whatever is necessary in order to protect yourself or your family. If a burglar has his back to you that isn't because he is running, it's because he hasn't seen or noticed you yet, and considering when he does he may then let all hell loose on you it is not excessve to incapacitate him while his back is turned. By walking into your house he has given up all right to any fair treatment, if he did not mean you some form of mental or physical harm he simply would not be there. I would put good money on you not being prosecuted or treated harshly for tackling any unknown intruder in that manner.