The European Union is set to block Sir Keir Starmer from securing a defence pact with the bloc by demanding deals on youth mobility and fishing rights at the same time.

It is an attempt by Brussels to revive a strategy by Michel Barnier, its former Brexit negotiator, aimed at preventing Britain gaining the upper-hand in any negotiations.

A senior diplomat said the EU’s negotiation team will insist on “parallelism” – where nothing is agreed until everything is agreed – in the Prime Minister’s proposed reset talks with Brussels.

This means that the Government’s desired security and defence agreement will be packaged together with EU demands for guaranteed access to Britain’s fishing waters beyond 2026 and a free movement deal for youngsters.