A jury has been discharged following its failure to reach a verdict on allegations that a police officer assaulted the former footballer Dalian Atkinson with a baton after he was felled by a stun gun on the night he died.

The case against Mary Ellen Bettley-Smith, a West Mercia probationary constable, ended with a hung jury a day after PC Benjamin Monk was convicted of manslaughter and told he would face an inevitable prison term.

The jurors at Birmingham crown court deliberated for more than 21 hours before telling the trial judge they would not be able to reach a verdict on the charge against Bettley-Smith of unlawful use of force even if they were given more time.

Bettley-Smith said during the trial that she had used necessary force to defend herself and others, but prosecutors claimed she had exaggerated the threat posed by the former Aston Villa, Sheffield Wednesday and Ipswich Town player to help Monk’s attempt to justify excessive force.

The jury was told during the six-week trial that Monk had fired a Taser weapon three times – including a single 33-second discharge – and left two bootlace prints on Atkinson’s forehead near his father’s home in Meadow Close in Telford in August 2016.

The jurors took 18 hours and 48 minutes to reach unanimous verdicts on Monk, who is believed to be the first police officer since 1986 to be found guilty of unlawful killing over a death in custody or following police contact in England and Wales.