British Foreign Secretary Philip Hammond said Monday that Iran is “too important a player” to leave it in isolation with sanctions on its controversial nuclear program – even while admitting there is no guarantee the Iranian regime won’t seek nuclear weapons.

Hammond made the comments to BBC just before meeting Iranian President Hassan Rouhani, in a meeting that comes a day after he reopened the UK embassy in Tehran that was trashed by Iranian rioters in 2011 who apparently acted under state guidance – Iran did not bother to cover up the graffiti reading “death to England” still scrawled on several places in the embassy.

The British diplomat said “we should tread carefully. There is a deep legacy of distrust on both sides, and we have major areas where we have very substantial policy differences, but that doesn’t mean we shouldn’t be talking.”

“We do see eye to eye on the need to interdict the opium traffic between Afghanistan and Europe, we do see eye to eye on the need to challenge ISIL,” he said, employing another acronym for Islamic State (ISIS).

Bilateral ties collapsed in 2011 when the UK conformed with UN sanctions against Iran’s nuclear program, and Iranians responded by storming the embassy.

According to Hammond, Britain would be able to influence problematic points in Iran – such as its abysmal human rights record – only once it reestablished diplomatic ties with the leading state sponsor of terrorism.

Hammond said the two countries will likely reinstate mutual ambassadors in the coming months, although Iranian Deputy Foreign Minister Majid Takht Ravanchi said Saturday that “we are not considering to send Iran’s ambassador to Britain.”

In an apparent admission, Hammond acknowledged there are no guarantees the Islamic regime won’t seek nuclear weapons in the future, but said “you have to make a judgement.”

“My judgement is that whatever Iran has or hasn’t been doing in the past, the regime, the Iranian people, have come to the conclusion that pursuing, or being believed to pursue, an illegal military nuclear program just imposes too great a cost on Iran,” he claimed.

Not isolating Iran via the deal, which gives it hundreds of billions of dollars in sanctions relief, is “the best bet for the future,” he added.

Rouhani just this Saturday vowed to breach the deal‘s limitations on weapons and rocket trade, and Iran has likewise promised to flout the deal further by holding ballistic missile tests.