If your affairs are simple, UK testacy law will suffice and the off-the-shelf wills can only complicate matters. If they are not simple, get a probate lawyer to do it for you.
Having said that, we did our own; but my wife is a solicitor and she got her firm's probate department to check it out
With the effect that fiscal drag has had in bringing even some of us normal people within the reach of Inheritance Tax, it would be sensible for property owners to get some advice in that area.