Electronic vapor provision system

1. An electronic vapor provision system comprising:

a vaporizer for vaporizing liquid for inhalation by a user of the electronic vapor provision system;

a re-chargeable power supply comprising a cell or battery for supplying power to the vaporizer, wherein the cell or battery is configured to be re-chargeable solely from a power source external to the electronic vapor provision system;

a sensor for detecting airflow through the electronic vapor provision system as a result of the inhalation by the user;

a manual activation device; and

a control unit for causing power from the cell or battery to be supplied to the vaporizer to vaporize the liquid providing the control unit determines that both (i) the sensor is detecting airflow through the electronic vapor provision system and (ii) the manual activation device is manually activated by the user,

wherein the manual activation device is configured to remain activated only for the duration of an ongoing, continuous operation from the user, and once the user operation terminates, the manual activation device is configured to automatically de-activate.

2. The electronic vapor provision system of claim 1 , wherein the vaporizer is a heater which is supplied with power from the power supply to heat and thereby vaporize the liquid for inhalation by the user.

3. The electronic vapor provision system of claim 1 , wherein the liquid comprises nicotine.

4. The electronic vapor provision system of claim 1 , wherein the sensor detects a pressure drop to detect airflow through the electronic vapor provision system.

5. The electronic vapor provision system of claim 1 , wherein the manual activation device comprises a button.

6. The electronic vapor provision system of claim 1 , wherein the manual activation device is a touch sensor.

7. The electronic vapor provision system of claim 1 , wherein the manual activation device is a slidable or rotatable switch for movement between a first position in which the manual activation device is deactivated and a second position in which the manual activation device is activated.

8. The electronic vapor provision system of claim 7 , wherein the switch is biased towards the second position in which the manual activation device is deactivated.

9. The electronic vapor provision system of claim 1 , wherein the sensor is mounted on a circuit board.

10. A method of operating an electronic vapor provision system including a vaporizer for vaporizing liquid for inhalation by a user of the electronic vapor provision system, wherein the electronic vapor provision system includes a re-chargeable power supply comprising a cell or battery for supplying power to the vaporizer, wherein the cell or battery is configured to be re-chargeable solely from a power source external to the electronic vapor provision system, the method comprising:

providing a manual activation device for user activation;

providing a sensor to detect airflow through the electronic vapor provision system as a result of the inhalation by the user; and

causing power from the cell or battery to be supplied to the vaporizer to vaporize the liquid provided that both (i) the sensor is detecting airflow through the electronic vapor provision system and (ii) the manual activation device is manually activated by the user,

wherein the manual activation device remains activated only for the duration of an ongoing, continuous operation from the user, and once the user operation terminates, the manual activation device is automatically de-activated.

11. The method of claim 10 , wherein the manual activation device is a button, touch sensor, or switch.