The Christmas deadline for the Covid-19 booster programme is expected to be missed.
The NHS is now planning to get third vaccine doses to all over-50s who want one by mid January, the Times reported.
The Labour Party claims current rollout rates mean it won’t be completed until the spring.
NHS bosses now believe older adults will not have been offered boosters until after hospitals have reached their busiest time of year.
It comes as NHS England is planning to open booster jab bookings a month early to speed up the rollout.
From next week, the NHS will send out Covid vaccine invites to people five months after their second jab instead of six so they can secure an appointment sooner.
The booster campaign has stalled in the past week, with the UK daily average of 278,053 a day about 14% lower than a week ago.
However in England there are signs the decline has been reversed, with 246,079 boosters yesterday taking the rolling average over 230,000 a day for the first time.
Labour has called on the Government to set a target of administering 500,000 Covid booster jabs a day.
Shadow health minister Rosena Allin-Khan told the Commons that the Government “just does not have a handle on Covid going into the busiest season for our NHS” even with the winter plan B, and said the UK needs to “turbo charge vaccine boosters”.
The medical doctor said: “On current trends we won’t complete the booster programme until spring 2022.
“The Government needs to get a grip and set a target of 500,000 boosters a day. At the moment the figures are less than 300,000.”
So far 7.3 million of the 11.5 million eligible in England have had a jab.
Some 30% of eligible over-80s have not had a third jab.
The NHS originally planned to complete boosters for all over-50s and younger vulnerable this year.
Ms Allin-Khan told MPs that she has been informed of people complaining they cannot get a booster appointment.
She said: “Local residents are contacting us saying they can’t get the boosters they so desperately need.
“One lady in her 70s who has underlying health conditions went to her pharmacy and called 119 just to be told she wasn’t eligible for a booster.
“She has now finally got one booked for December but had to rely on her daughter to book the appointment for her because she doesn’t use the internet. The system simply isn’t working.”
She added: “The Government had a deadline of November 1 to offer booster jabs to all care home residents.
“Right now only 23% of care home residents in Leicester have had their booster jab with the picture across the country extremely patchy.”
Vaccines minister Maggie Throup told MPs more than 650,000 12 to 15-year-olds have been vaccinated “since launching the programme in September”.
“We are also rapidly rolling out our booster programme to give people the best protection over winter and help reduce pressures on the NHS,” she added, with eight million people across the UK having “now received the vital protection a booster dose provides”.
