For complaints about NHS services there are supposed to be advice/advocacy services called Independent Complaints Advocacy Services, ICAS for short, which will provide support and information to patients , relatives, carers etc. These exist across the country and partially replace the former providers of independent advice, Community Health Councils, which were abolished in December 2003. Go to
http://www.dh.gov.uk/PolicyAndGuidance/OrganisationPolicy/ComplaintsPolicy/NHSComplaintsProcedure for more information.
PALS services can be good too, but remember that their staff are NHS employees and not independent of the service you may wish to complain against. Some are distinctly better than others. Some can be a bit slow to respond or simply give fairly basic advice, not always the most useful.
For complaints against care homes, there should be in house complaints procedures which should be available to residents and relatives. Use these procedures before any other route. Going to an MP may be helpful subsequently, as Norman says. The Commission for Social Care Inspection,
www.csci.gov.uk
will also pick up on complaints against homes where you feel the reply is unsatisfactory or has been late in coming.
Now a note of caution which may seem to contradict the above advice. My experience of care homes has been that even a hint of discontent may antagonise them, and in my relative's case resulted in her ultimate loss of her place there. Be very careful how you raise your concerns, especially if there is any likelihood that the management would like to evict. They can and do do this, usually on the basis of 'not being able to meet the person's care needs'. Don't give them an excuse to do this.
For services provided by local authorities, there will also be formal complaints procedures which clients and their carers and relatives can and should use.
For both NHS and Local Authority complaints, there is a level of appeal through an Ombudsman. Go through the local procedure first though as Ombudsmen offices do not consider complaints which have not been pursued at the lower layer first.