A staff member at a coronavirus testing centre was assaulted when a group of anti-vax protesters stormed in, police said.
Detectives gave more information about the incident on December 29 in Milton Keynes.
They released a photo of a man they want to question regarding the assault.
The middle-aged man may have ‘vital information’ about the attack on a member of staff.
A 58-year-old man has already been arrested on suspicion of other offences which happened as the anti-vaccination protestors barged into the centre, dismantled equipment and caused criminal damage.
A spokesman for Thames Valley Police said on Saturday: ‘We are releasing an image of a man who we believe may have information in connection with an assault.
‘Between 2.45pm and 2.56pm on December 29, a member of staff, a man aged in his 20s, at the Covid-19 testing centre in Second Street, Milton Keynes, was assaulted.
‘He was not injured in the incident.’
Chief Inspector Graham Hadley of Thames Valley Police, said: ‘We continue our investigation with regards to the protest at the Covid-19 testing centre in Milton Keynes.
‘We are releasing this image as we believe this man may have vital information with regards to the assault. If you recognise this man or if this is you please contact Thames Valley Police on 101.
‘If anyone wishes to remain anonymous, you can contact the independent charity Crimestoppers by calling 0800 555 111 or via their website.’
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