Who are the main characters in As Time goes by?

* Lionel Hardcastle, a self-employed builder with an office at home, and a bachelor.

* Jean Pargetter, a widowed owner of a department store.

* Alistair Mackenzie, a doctor of medicine, married to Susan.

* Sandra Cartwright, a divorced friend of Jean's, who later marries Tom (who is killed off between seasons 4 and 5) and then marries David (who is killed off between seasons 6 and 7).