Electronic vapor provision system

An electronic vapor provision system comprising:

• a first unit comprising a battery or cell;
• a second unit comprising a heater and a nicotine source for producing nicotine vapor when heated;
• wherein the first unit and the second unit comprise a bayonet fitting for providing a mechanical and electrical connection between the first and second unit, wherein said electrical connection allows the battery or cell to provide power to the heater to produce nicotine vapor from the nicotine source;
• wherein the electronic vapor provision system has a longitudinal axis, and the bayonet fitting is configured such that the first and second units are connected by:
• relative movement of the first and second units along said longitudinal axis to a first engagement position;
• and
• relative rotation of the first and second units about the longitudinal axis from the first engagement position to a final engagement position that prevents both (i) relative movement of the first and second units along said longitudinal axis, and (ii) relative rotation of the first and second units further away from the first engagement position;
• and wherein the bayonet fitting further includes a biasing means that provides a rotational bias to prevent rotation of the first and second units from the final engagement position to the first engagement position.