The Delta variant now represents 91% of new cases in the UK, Health Secretary Matt Hancock has told MPs.
Mr Hancock has said the current data shows the Delta variant, which was first identified in India, is now responsible for the majority of positive Covid cases in the UK.
The health secretary was questioned over allegations made by the Prime Minister's former aide Dominic Cummings to the Health and Social Care Committee and Science and Technology Committee.
Mr Hancock told MPs this number was from an assessment he saw "last night".
His comments come just a week after Public Health England warned there is early evidence to suggest there is a "significantly increased risk of hospitalisation" from the Delta variant in comparison to the Alpha strain.
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Mr Hancock also suggested lockdowns and social distancing could return if there was a new coronavirus variant that majorly escaped existing vaccines.
He said: "The plan is predicated on having a variant vaccine as fast as possible. The Prime Minister has set a target of having a variant vaccine and treatment and diagnostics within 100 days but we’re not there yet at that speed."
The health secretary said he is "highly confident" that vaccine would be developed quicker than previously.
"In the meantime the tools we have at our disposal are the tools that are available," he added.
He did not deny the plans include lockdowns and social distancing requirements when asked.
Health Secretary Matt Hancock gives evidence to MPs
Mr Hancock also said he would "consider" publishing the playbook for dealing for a new strain that escapes vaccines so it can be scrutinised.
"Writing a plan for absolute vaccine escape is essentially writing a plan for a new pandemic," he added.
Meanwhile, the number of Covid-19 cases reported across the UK was at the highest it has been since the end of February on Wednesday, jumping by 7,540 in the past 24 hours.
There have now been 4,535,754 confirmed coronavirus cases in the UK since the start of the pandemic.
The figure reported in the 24 hours to 9am on Wednesday is the highest since February 26 when 8,523 cases were reported - more than three months ago.
The latest figures from the government showed a further six deaths among patients who died within 28 days of testing positive for the virus.
It means the UK's death toll as of 9am on Wednesday now stands at 127,860.