Yes, people in the U.K illegally cannot register to use NHS .
There are people who are officially homeless , but have an address and can register with a G.P.
Also people who registered with a G.OP before they became homeless, can still use their G.P .
People can find dentists everywhere , but they have to pay for it .
You can still find NHS dentists , but many private dentists do not accept new NHS patients , that could be because the NHS only pays for a basic service and dentists prefer private patients