(The opinions expressed here are those of the author, a columnist for Reuters.)

LONDON, June 7 (Reuters) - Reports of Britain being on the verge of a current account crisis are almost always greatly exaggerated but the second half of 2017 could be the hardest time for years to convince overseas investors that they should keep on plugging the yawning deficit.

Economic growth is slowing, Brexit uncertainty will crystallise as negotiations over Britain’s departure from the European Union get under way, and the relative yields on offer to foreign buyers of UK gilts are the lowest in decades.

Having one of the developed world’s biggest current account deficits means Britain relies on “the kindness of strangers”, in the words of Bank of England (BoE) governor Mark Carney, to balance its books.

Last year the deficit was 4.4 percent of gross domestic product, meaning Britain needed about $100 billion from abroad.

The shock Brexit vote a year ago did not cool demand for gilts from overseas investors immediately. They kept buying but demand peaked in November at a three-month rolling rate of nearly 40 billion pounds ($50 billion) a month. That was the highest since BoE records began in 1986.

Gilt investors often include foreign reserve managers at central banks and sovereign wealth funds, with long-term horizons and deep pockets. They are prepared to ride out short-term volatility if they see longer-term value.

They are unlikely to cut and run just because of Brexit and slowing growth. If anything, sterling’s 12-percent fall since June last year will have fuelled more purchases just to maintain the currency composition of their FX reserves.

But appetite for gilts at any price is not unlimited, particularly from sovereign wealth managers, who are more sensitive to rates of return than reserve managers. Since November, foreign purchases of gilts have waned and the rolling average for most of this year has been a small net outflow.

State Street Global Markets’ EMEA head of macro strategy, Tim Graf, believes foreign demand is the “swing variable” for financing the current account. Worryingly, that demand may be about to dry up, he said.

FEEL FLOWS

You can see why. Returns offered by gilts seem low in light of the potential risks ahead. Official interest rates are a record low 0.25 percent and the 10-year yield is back below 1 percent, the lowest since October.

The difference between British and the G3 - U.S., German and Japanese - average 10-year yield is about 17 basis points, close to the lowest in decades, according to State Street.

Meanwhile, inflation is 2.7 percent - already above the BoE’s 2 percent target - and rising, putting the squeeze on real earnings, consumer spending and overall growth.

This comes just as the Brexit uncertainty is set to crank up a level irrespective of the outcome of this week’s national election and break-up talks with the EU begin in earnest.

“The risk is for reduced inflows in the short run and potential outflows over the long run. That’s a worry for me,” Graf said.

And it is not just bonds. According to Office of National Statistics data, foreign investors sold a net 60 billion pounds of UK equities in the fourth quarter of 2016, their biggest single quarterly sales on record going back to 1980. On a four-quarter rolling basis the total outflow was 114.5 billion pounds, also the biggest fourth quarter outflow on record.

Mutual fund flows data from EPFR Global show that cumulative UK equity fund inflows have evaporated since the start of last year. Outflows are now the largest for years.

Meanwhile, a report this week by asset manager Invesco showed that sovereign investors view Brexit as a significant risk for all UK investments.

The study, based on interviews with 97 sovereign wealth funds, state pension funds and central banks with assets in excess of $12 trillion, showed that Britain saw the biggest drop in attractiveness, scoring 5.5 out of 10 versus 7.5 last year.

Some 41 percent of sovereigns expect to introduce new underweight positions to UK assets in 2017, compared with just 5 percent planning new overweight positions. A majority of 54 percent said they would not make any changes to their weighting, preferring to wait to assess the longer term impact of Brexit.

But foreign investors do not need to sell UK assets for current account funding - and therefore sterling - to come under pressure. They just need to buy less, or not buy at all.