Taken directly from the FA's handbook:
For the purposes of determining handball offences, the upper boundary of the arm is in line with the bottom of the armpit.
Handling the ball
It is an offence if a player:
• deliberately touches the ball with their hand/arm, including moving the hand/arm towards the ball
• scores in the opponents’ goal directly from their hand/arm, even if accidental, including by the goalkeeper
• after the ball has touched their or a team-mate’s hand/arm, even if accidental, immediately:
• scores in the opponents’ goal • creates a goal-scoring opportunity
• touches the ball with their hand/arm when:
• the hand/arm has made their body unnaturally bigger
• the hand/arm is above/beyond their shoulder level (unless the player
deliberately plays the ball which then touches their hand/arm)
The above offences apply even if the ball touches a player’s hand/arm directly from the head or body (including the foot) of another player who is close.
Except for the above offences, it is not an offence if the ball touches a player’s hand/arm:
• directly from the player’s own head or body (including the foot)
• directly from the head or body (including the foot) of another player who is close • if the hand/arm is close to the body and does not make the body unnaturally
bigger
• when a player falls and the hand/arm is between the body and the ground to
support the body, but not extended laterally or vertically away from the body
So in the case of Lokonga, the ball striking the players arm is not a handball because the guys's hands were down by his side, not in an unnatural position, they didn't make his body bigger.