There are clear regulations about what you can and can't do electrically and who is competent to do so. However, as far as I'm aware it's still very much buyer beware re wiring much like the depth of the structural survey that will be done as a requirement for the lender. Very few houses will meet current regulations as the regs are updated all the time and are not retrospective and it doesn't necessarily mean they are dangerous. So in answer to your question, yes, if you don't get the wiring checked before purchase it's very easy to buy a lash up. If you did identify work that needed doing you may want to factor that into the purchase negotiations. If you are selling and you have concerns, at least for your own safety get it checked to ensure there is nothing dangerous.