According to The Telegraph, the police are not letting people in or out of the Prime Minister's offices at Downing Street due to the incident.
Earlier on Thursday, it was reported that Theresa May was due to meet her cabinet ministers for further discussions on the Brexit deal.
Temporary road closures in place around Whitehall whist suspect item assessed. Police attended at 1201hrs today. Specialist officers are now in attendance. Thank you for your patience— MPS Westminster (@MPSWestminster) 23 мая 2019 г.
— Sotiri Dimpinoudis (@sotiridi) 23 мая 2019 г.
Moments later, the police informed the public that the roads will be reopened soon:
Happy to update the item concerned has now been fully assessed and deemed non-suspicious. Roads will be reopened shortly. Thanks again for your patience and cooperation— MPS Westminster (@MPSWestminster) 23 мая 2019 г.