A TT electrical system has no incoming earth wire with the mains supply to the house. The earth is normally provided via a long metal spike in the ground; it sounds like your problem is associated with this.
I have known similar problems occur due to long dry spells � soaking the ground at the earth spike normally cures things.
Given the importance of having a reliable earth connection, I would advise that you get is sorted ASAP. Get 3 quotes for the job, that way you can be reasonably sure that you are not being ripped off.
In older wiring (very old), it was common not to insulate the earth conductor (bare wire), this suggest the person who rewired the house 8 years ago, may have cut corners.
Having a bare earth wire is not necessarily a major issue. What I suspect the electrician is proposing to do, is to place a short length of insulation over the bare earth wire at each socket termination, where it could come into contact with the Live or Neutral connections (of the socket). If you take the view that nothing will cause the bare earth wire to contact Live or Neutral, then there will be no problem.
(�75 for 3 hours sounds very reasonable)