I've bought an old house, will it require rewiring?

Not all houses will require a full rewire. It may have been upgraded at some point. The first place  to look is the fuseboard. If it has pull-out fuses then this may be a sign of the electrical installation being dated.

It will be worth getting in contact  with  local electrician  to carry out a safety inspection.  This willl check the current electrical installation via visual and electrical tests.  A professional judgement can then be made on the state of the electrical install.