Primrose Hill journalist Baroness Dame Joan Bakewell is threatening the government with legal action over delays to the second dose of the Covid-19 vaccine.

The Labour life peer and TV presenter said there were grounds to show the decision taken by ministers to delay the second dose of the Pfizer/BioNTech vaccine by up to 12 weeks was unlawful.

Originally, those having the jab were told their doses would be given 21 days apart but the government has now stretched the timeline for the second dose to between three and 12 weeks.

It did this following a recommendation from the Joint Committee on Vaccinations and Immunisation (JCVI) to give more people a first dose of the vaccine.

Baroness Bakewell, 87, has instructed the law firm Leigh Day to start proceedings in response to the new dosing policy, and names the respondent as Health Secretary Matt Hancock.

The Leigh Day letter, marked “Urgent: Proposed claim for judicial review”, says: “Our client is fully supportive of the national effort to meet the exceptional challenges posed by the pandemic.

“Our client is, however, concerned that the Government’s instruction to delay the provision of the second dose of the Pfizer vaccine is potentially unlawful and unsafe and would therefore impede rather than advance the pandemic response.”

Baroness Bakewell, who received her first dose of the Pfizer vaccine in December, said: “Older people are in limbo: they need to know whether delaying the Pfizer vaccine is both safe and legal.

“I am bringing this case because I believe the Government needs to make this clear.”

The move follows disquiet among some scientists about the 12-week delay, while Pfizer recommends the second dose of its jab is given after 21 days – as set out in its clinical trials.

A Department of Health and Social Care spokesperson said: “Getting vaccines deployed as rapidly as possible to as many at risk older and clinically vulnerable people, as well as frontline health and social care workers, is our number one priority.

“The decision by the MHRA to change vaccine dosage intervals followed a thorough review of the data and was in line with the recommendations of the UK’s four chief medical officers.

“The government is closely following the guidance of the Joint Committee on Vaccination and Immunisation (JCVI) which recommended we prioritise first doses of vaccine for as many people as possible initially.”