The first proper test of Theresa May's premiership has come - predictably enough - totally out of left field (ha ha - welcome to No. 10 Mrs May).

It is the £24bn takeover of ARM, the UK's ONLY world leading hi-tech electronic company, by SoftBank of Japan.

The point is that her sole proper policy speech since announcing she wanted to become PM - the one she gave in Birmingham just a week ago - was completely unambiguous that she opposed foreign companies buying our strategically important businesses.

She cited Cadbury, which was acquired by Kraft of the US, and AstraZeneca, which narrowly escaped takeover by Pfizer. Both would have been blocked by her, she suggested.

SoftBank's takeover bid has been welcomed by Prime Minister Theresa May and Chancellor Philip Hammond. Credit: Reuters

Well she now has an opportunity to put her mouth where Japanese money is. What will she say about the surrender of ARM?

She cannot pretend it does not matter. ARM designs chips that go into billions of connected devices, from iPhones to a new generation of internet-linked household products.

It is at the heart of Cambridge's hi-tech research and manufacturing cluster. It supports jobs and knowledge well beyond the 3,000 plus it directly employs there.

No other UK tech company has its reach or reputation.

What's more, one very important reason why the UK is economically fragile post Brexit is our unsustainably large current account deficit which is due - in part - to decades of selling our industrial jewels to foreigners, who have been siphoning profits and dividends earned here to other parts of the world.

So surely, you would say, May must oppose the ARM takeover as proof she is starting a new chapter in the UK's economic stewardship - an end to the hollowing out of our better-paying industries - which is what she claims.

Pro-Brexit cabinet figures like Boris Johnson are also expected to hail the ARM takeover as good business for Britain. Credit: PA

Well maybe.

She will be hearing a different argument from the more conservative officials in the Treasury and Downing Street, and from her more Brexit-loving ministers.

The Treasury will fret that, outside the EU and its single market, we cannot risk creating the perception that we are hostile to investment by foreigners after all these years - because that way lies the risk of capital deserting these shores and consequential penury.

Meanwhile the likes of Boris Johnson, David Davis and Liam Fox will doubtless argue that the ARM takeover is a vote of confidence in our supposedly glorious economic prospects outside the EU.

So this is a huge test of May, right at the start of her premiership. Will she measure up?

UPDATE: 10.20am

Well it didn't take long for May and her Chancellor Philip Hammond to be captured by Treasury orthodoxy.

They have welcomed the sale of ARM to SoftBank, with Hammond claiming it will turn this "great British company into a global phenomenon" - which, some would say, is to cynically ignore that it already is a global phenomenon.

May has obviously decided to go with the spin that Brexit hasn't turned off successful overseas investors from investing here.

But this is to gloss over that the Brexit-induced collapse in sterling makes our crown-jewel assets cheaper to foreigners than they've been in many years.

As I mentioned earlier, if the government simply waves through a stream of opportunistic takeovers of our great companies while sterling is on the floor, our capacity to ever again pay our way in the world will be fatally holed.