I would argue potentially indefinitely (or at least until the electrician died, or a company ceased to exist, and no directors etc could be held liable in law), if it can be shown that the electrician was negligent, and that negligence resulted in loss or injury.
Let’s say the electrician used incorrectly rated wiring – which at some later date was shown to be the source of a fire. Of course, you would have to show that it was the electrician that used the wrong wire.
A possible mitigating defence open to the electrician would be that it is reasonable for you to have the electrical installation checked regularly. In such an instance, to strengthen your case, you would have to show this had been done – and that those checks would not routinely highlight the negligence of the original electrician.