For the purposes of the aircraft technical log the ANO says
11 (1) A technical log shall be kept in respect of every aircraft registered in the United
Kingdom in respect of which a certificate of airworthiness in either the transport or in
the aerial work category is in force.
(2) (a) Subject to sub-paragraph (b), at the end of every flight by an aircraft to which the
provisions of this article apply the commander of the aircraft shall enter:
(i) the times when the aircraft took off and landed;...........
In our group we record and pay for take-off to landing times. In respect of the personal flying log book the times to be recorded are different, as FF says.
It is my practice to add 5 mins at the beginning and end of each flight (total 10 mins per flight to allow for taxying, holds runup etc. I believe many flying clubs also use the same system, i.e. the figures in the a/c tech log are 10 mins less than what is paid for (most charging chock to chock).
Mike