Games can only be rated if they are played under acceptable conditions, with clocks.
Lightning, Correspondence and Online games are excluded.
It is required that:
a. The FIDE Laws of Chess are used, as modified by the ECF Competition Rules.
b. A game will be rated if both players make at least one move. Defaulted games, byes and absences will not be rated.
c. One of the following rates of play is complied with:
Each player must have at least 10 minutes, and less than 60 minutes, for all moves. This includes both the initial time control and any subsequent time controls or quickplay finish. When Fischer (cumulative) mode is used, the time available for each player is calculated on the assumption that the duration of the game is 60 moves.
Each player has more time than the maximum defined above for Rapidplay.
Of course events must conform with the ECF's Membership and payment requirements. Events are rated as reported by the organisers; they are not accepted from individual players. There is one exception to this: results can be accepted from individual Direct Members in otherwise unrated events which are played outside England. See Rating games played abroad.
Yes. ECF Membership is not a requirement for a published rating.