Dynamic modelling suggests that the number of people who are protected against Covid-19, either because they are naturally immune or have received a vaccine, will hit 73.4 per cent on April 12.
Figures published by the Office for National Statistics last week - based on antibody testing - show that around 54 per cent had antibodies by March 14.
Since then, a further 7.1 million people have received a first jab, while nearly 100,000 more people have tested positive for Covid-19.
In addition to this around 10 per cent of the population is naturally immune, either through exposure to other coronaviruses or because they have T-cells, which would not be picked up in antibody testing.
Professor Karl Friston, from UCL, said: “The herd immunity estimates surprised me. However, they are unremarkable when one considers that over 50 per cent of adults have been vaccinated, around 42 per cent of people have now been exposed to the virus and about 10 per cent have pre-existing immunity.
“When factoring in the estimated efficacy of vaccination in terms of sterilising immunity, this – according to the model – means about 70 per cent of the population are immune.
“Based upon contact rates at the beginning of the pandemic and estimated transmission risk, this is nearly at the herd immunity threshold.”
The data, seen exclusively by the Daily Telegraph, is in stark contrast to modelling published earlier this week by Imperial College London, which suggested only 34 per cent of the population was immune by the end of March.
UCL’s work is different to other models because it reacts to real-time deaths, infections, vaccinations, vaccine effectiveness data and Google mobility trends with inform transmission trends, the paper reported.
The university also predicted that the threshold level needed for herd immunity will drop dramatically in the next couple of months with the UK needing just 40 per cent protection by the middle of the summer to be safe.
The study comes just over a week after lockdown restrictions were eased to allow people from 6 households to mix outside.
On Monday they will be eased further, with non-essential shops, gyms and leisure centres reopening for the first time in months.
Pubs and restaurants will also be able to serve meals outdoors.
Latest figures show 31.7 million people have been vaccinated, with 5,683,509 receiving a second jab.