Should you need a doctor to visit you at home during the night, most doctor's surgeries have an answering service which will give you the relevant number to call. Contraception, advice on pregnancy termination's and free supplies of condoms, pills, coils, etc. can be obtained from your local family planning clinic. Check for your local clinic in the phone book. Appointments are usually not necessary but some operate only a few days a week so find out their schedule. Most clinics also offer free and confidential HIV testing and counseling.
Some dentists offer free check-ups, but treatment can be expensive.
It is a free walk-in emergency dental hospital for anyone without a dentist in London. No appointment is needed, and people are treated on a first come first served basis. Its open 9am to Noon, and 2-4pm, Monday to Friday. It's not a bad idea to have your childhood shots boosted, plus Hepatitis A and Tetanus. Ask for a vaccinations certificate as some countries require these before they will let you enter.