I have to recommend Patrick & Rick who sweep and survey chimneys on all our refurbishment projects. It is critical to have the survey done once in a chimney's lifetime, to ensure that your flue is correctly constructed, clear of concrete / mortar and safe to use.
Any person purchasing a house would be recommended to get this service done as part of your pre-signing survey. A faulty chimney is lethal, and expensive to rectify if a new liner can not be installed.