Health Secretary Matt Hancock said at least 60 different local authorities in England have recorded Covid infections caused by the new variant.
He said the World Health Organization had been notified and Porton Down was doing detailed studies.
Mr Hancock said there was “nothing to suggest” it caused worse disease or that vaccines would no longer work.
He told MPs in the House of Commons that over the last week, there had been sharp, exponential rises in the virus across London, Kent, parts of Essex and Hertfordshire.
“We’ve currently identified over 1,000 cases with this variant predominantly in the South of England although cases have been identified in nearly 60 different local authority areas.
“We do not know the extent to which this is because of the new variant but no matter its cause we have to take swift and decisive action which unfortunately is absolutely essential to control this deadly disease while the vaccine is rolled out.”