No earthing wire in metal switch

I would suggest an EICR to be carried out on the installation first. Then it can be ascertained what is actually wrong with it. To just suggest a rewire straight out is to say the least, scare tactics.

I would personally get a test done to just check to see if it is twin and earth cable and the earth has been cut out if that I the case and you can get access to it you can extend the earth cable to the back box then from the back box to the switch so you don't only earth the switch but the back box is also earthed in which the screws go into Hope this helps

Metal fittings, whether they are switches or lights needs to be protected with a cpc (earth). Given your backbox is wooden it would suggest old wiring i.e. 70s and earlier, which may be indication there is no earth. What colours are the wires: red & black or brown & blue? This will give an indication of the period. You have 4 possibilities: 1. change the metal switch to plastic. No need for earthing. 2. have an electrician inspect the wiring behind the switch to see if the earth has been snipped off and then can be reconnected. This may lead to option 3 3. get an EICR which will highlight if that circuit has earth or not, or indeed if that run of cable has earth in it or not 4. get that circuit rewired