Another source said Britain asked for the delay to let May set out London's latest views and plans on Brexit before more negotiations. It is the sixth position paper by the Government in its talks with Brussels.
Britain has bigger defence and development budgets than any other European Union member state and its diplomatic and intelligence services are among the most extensive in Europe.
European Parliament Vice President Mairead McGuinness, who is a member of the parliament's Constitutional Affairs Committee, said a proposal has been discussed which outlines a reduction in the total number of MEPs but proposes additional seats for certain countries including Ireland.
"However, the European Parliament has made it clear that, whatever the outcome of the negotiations on the future European Union-United Kingdom relationship, they can not involve any trade-off between internal and external security, on the one hand, and the future economic relationship, on the other hand". Brexit secretary David Davis said the position paper would highlight Britain's desire to use its assets and capabilities in partnership with the EU.
Foreign Secretary Boris Johnson has offered Brussels "a future partnership with the European Union of depth and breadth, taking in diplomacy, defence and security, and development" in an article for The Times. "It's vital. We are not making threats", he said.
The Guardian newspaper said the latest paper "strikes a more positive note about European Union defence and foreign policy matters than expected".
The legislation repeals the 1972 Bill which brought Britain into the European Economic Community and translates all EU rules into British laws.
It is the next step in implementing last year's historic referendum vote to leave the European Union, after Prime Minister Theresa May formally notified Brussels of Britain's withdrawal in March. Criticism of the Bill has focused on the use of Henry VIII clauses to allow ministers to amend laws, with one Labour MP describing parts of it as "clauses Erdogan, Maduro and Putin would be proud of".
"We want to fight terrorism together".