Make-or-break moment?

♦ Johnson’s option is to sign UK up to a US-led alliance outlined by Trump admin

♦ That decision could boost UK’s chances of striking post-Brexit deal with US  

Iran’s seizure and continued detention of a UK-flagged tanker deals Boris Johnson an immediate loyalty test: Britain’s new prime minister may have to choose between Gulf escorts led by Europe or by the United States.

Which way Johnson leans could set the tone for a complex agenda that includes withdrawing from the European Union and striking a trade deal with the United States.

It could also maintain or break European efforts to keep alive the deal curbing Iran’s nuclear ambitions that Washington pulled out of last year.

Some US commentators see this is a make-or-break moment for Europe’s policy on Iran as a whole.

“Johnson could simply announce that the UK is joining America’s maximum-pressure campaign and calls for a new (Iran) deal,” the editorial board of The Wall Street Journal wrote.

“The rest of Europe would likely have no choice but to join its Anglophone partners -- and finally present a united front.”

The idea of a European-led mission in the Gulf is carried over from a meeting chaired by Johnson’s predecessor Theresa May this week.

Britain has proposed that European partners join together in a “naval protection mission” to ensure commercial ships can safely navigate in the Gulf.

But such an operation would expose Britain’s continued reliance on EU allies at the very same time that Johnson is determined to yank his country out of the bloc on October 31.

Johnson’s other option is to sign Britain up to a US-led alliance outlined by Donald Trump’s administration at Nato last month.

That decision could boost London’s chances of reviving stalled efforts to strike a post-Brexit trade deal with Washington.

The downside risk is that British warships could be caught up in more aggressive US rules of engagement that London currently does not support.

The US president cheered Johnson’s election -- referring to him as “Britain Trump” -- and a source close to Johnson told The Daily Mail it was time to “reset” US-UK ties.

Yet that might doom British efforts to salvage the remnants of the 2015 deal with Iran that Trump pulled out of last year.

Tehran’s ultra-conservative Resaalat newspaper published a cartoon Wednesday of Johnson as a British butler being patted on the head by Trump.

Centre for European Reform foreign policy director Ian Bond said Johnson might actually win Trump’s favour by shepherding European navies to the Gulf. Bond said Johnson’s Brexit credentials might also be saved by the likely inclusion in this “coalition of the willing” of non-EU members such as Norway.

But Chatham House’s Middle East researcher Sanam Vakil advised Britain’s new leader to “avoid the temptation to align completely with Washington on Iran”.