A British toddler will be forced to spend her second birthday apart from both of her parents after her mother was detained and held without charge by Iran's Revolutionary Guard.
Richard Ratcliffe, from West Hampstead, London, will celebrate his daughter Gabriella's big day from 3,000 miles away at a protest party in west London near the Iranian embassy.
He has described his sadness at having to sing her happy birthday via Skype but says he hopes the action will help pressure authorities to free his wife and reunite his family.
Mr Ratcliffe will also attempt to present a card to the embassy at 1pm and ask that they pass it on to his daughter, who is being cared for by her Iranian grandparents.
"I kind of want to try and make it reasonably celebratory as well, so it's not too sad," he said of the teddy bears' picnic event in Hyde Park.
Mr Ratcliffe's wife Nazanin Zaghari-Ratcliffe, a British Iranian charity worker, was seized at Tehran airport as she tried to return to London with their daughter after a family holiday in April.
Gabriella, aged 22 months at the time, had her British passport confiscated and was sent to live with grandparents while Ms Zaghari-Ratcliffe was held in prison.
The toddler can only be collected and returned by England by her mother or father under Iranian law - but Mr Ratcliffe has been strongly advised not to travel at present.
He will host the picnic for his daughter as part of his Free Nazanin campaign. A petitionhas already gathered 750,000 signatures.
Mr Ratcliffe said the support from other families had been "really moving" adding: "In my bones, I feel it is that kindness that will in the end bring them home."