Thanks Su it certainly does this part put's it clearly in the first link
Does the law protect me? What is 'reasonable force'?
Anyone can use reasonable force to protect themselves or others, or to carry out an arrest or to prevent crime. You are not expected to make fine judgements over the level of force you use in the heat of the moment. So long as you only do what you honestly and instinctively believe is necessary in the heat of the moment, that would be the strongest evidence of you acting lawfully and in self-defence. This is still the case if you use something to hand as a weapon.
As a general rule, the more extreme the circumstances and the fear felt, the more force you can lawfully use in self-defence.
And in the same link this bit highlights how the area becomes greyer
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.
That is the quandary for the prepper for in "Home Alone" Kevin McAlister although a minor set traps to protect himself and his property, doing much damage along the way and much to our amusement, if you step that up to a more adult version, who knows it could be where they got the idea for the comedic one and did a "Death Wish" house of fun, then clearly you could finish up in trouble.
That said we can now progress slightly to the bat behind the door scenario, for in this instance you are not setting a trap are you? I would looking at the legalities say that you being a cautious prepper type have merely attempted to give yourself a fighting chance if attacked in your own doorway (whether a long bit of wood is appropriate in a space likely to be inadequate to swing it is another matter) beyond that and as a first line of defence escalating to projectile firing articles could be a step too far toward the Death Wish end of the scale, but further back into the property if entry has been forced regardless of yours and your families presence and by that point it is clear that those attacking have no problem hurting you, then even now all bets are off and the threat of lethal force is legitimate and if you happen to have a Bat'leth (Mr Worf's pointy thing) hung up in your passageway even better if you can curse in Klingon they can leave or have a bad day
One of my main concerns for all of us peace loving individuals who happen to like pointy things or shooting from catapults through to long range rifles, few of us actually practice using any of it/them in a defensive manor, and this is why an ex service person or survivalist having done a good deal more than entertained the possibility of having to defend oneself in any situation, can inadvertently appear the aggressor when defence of the person or home is discussed, these links, and this discussion, are valuable reference to help any of us gain a sense of balance in the here and now, in order to remain UK not Doomsday preppers.
I have a strategy, it's not written in stone, nor can it be, this scenario has too many variables, everything about it depends on those variables, being specific is not possible.
as well as the electronic repellents 
