Britain expects to receive its first doses of the vaccine made by US company Moderna within weeks, a minister said on Sunday.
The EU has toughened restrictions on exports and Britain faces a significant reduction in supplies in April with a delayed delivery from India.
“We expect that in April Moderna will come,” Culture Secretary Oliver Dowden told BBC Television.
The UK has inoculated more than half the adult population using vaccines made by Pfizer and AstraZeneca.
Its programme is critical to plans to reopen an economy that last year had its deepest contraction in three centuries.
Mr Dowden said the government was on track to offer first doses of a vaccine to all aged over 50 by the middle of April, and to the rest of the adult population by the end of July.
There is no danger of people being unable to get their second dose of the same vaccine within 12 weeks, he said.
The UK government is preparing to relax some lockdown restrictions on Monday.
People will be able to meet outdoors in greater numbers and outdoor sports centres such as tennis and basketball courts will be permitted to reopen.
The aim is to remove remaining restrictions on social contact from June 21.
Britain and the EU are in talks to resolve a stand-off over vaccine sharing as the bloc tries to get its own immunisation programme back on track.
Last week, the two sides indicated progress in defusing the dispute.
“We continue to have constructive discussions with the EU,” Mr Dowden said.
“Our position is very clear. The EU should not be engaging in blocking exports” and contracts should be honoured, he said.