IT was difficult to escape the feeling it might not be the best of weeks when the first thing to catch the eye on the Monday morning train journey was an animated Boris Johnson looking out of the front page of a discarded free newspaper. And this sense of unease proved well-founded.

The coverage, of course, was of the London Mayor’s announcement on Sunday that he would be pushing for the UK to exit the European Union.

Mr Johnson’s perhaps unsurprising declaration has come at a time when the polls have been showing the “out” camp developing a lead among the UK electorate. Interestingly, the opinion polls have been showing a clear majority of Scots preferring to remain in the EU, but more of that later.

Following Mr Johnson’s move into the limelight, the pound plummeted through the $1.40 mark to its weakest level against the US currency since 2009, during the Great Recession.

Those who believe exiting the EU would have no significant detrimental impact on the UK economy should take a close look at the pound’s tumble this week. This fall has had everything to do with increased fears in financial markets of so-called Brexit, with Mr Johnson viewed as an influential figure for many people in the UK.

The EU referendum is absolutely the last thing that the economy in Scotland or the UK as a whole needs right now. Scotland continues to be hit hard by the global oil and gas sector downturn. And the overall UK economy remains weak, with unbalanced, below-trend growth.

While David Cameron might now be pitted against Mr Johnson, we should remember it was the Prime Minister who chose to have a referendum on EU membership in the first place. Was such a referendum really necessary?

Mr Cameron has now got his revised terms for the UK’s membership of the EU and wants to stay in. However, the revised deal, regardless of its merits or otherwise, may well make little difference given that much of the general debate seems to be revolving around ill-informed talk and views about migration.

Sadly, the UK-wide polls seem to be indicating a lack of thought about the impact of an EU exit on the country’s exports. And what about the likely slump in foreign direct investment in the UK in the event of a vote to leave the EU? Surely companies from outwith the EU looking to gain easy access to the huge free trade bloc by setting up European operations would not be inclined to put them in the UK in the wake of a Brexit result?

Martin Temple, chairman of engineering and manufacturing employers’ organisation EEF, this week warned that leaving the EU would take Britain into “an abyss of uncertainty and risk”. He is right to use such language. After all, the sad fact of the matter is that the polls are showing a very real risk of a vote to leave the EU in the referendum on June 23.

Scottish business leaders, in various surveys, have made it plain that they see major benefits for their firms and the overall economy north of the Border from EU membership.

The extent to which the Scottish economy is currently under pressure from oil and gas sector weakness was underlined again this week.

Industry body Oil & Gas UK warned North Sea exploration remained at an all-time low, with no sign of improvement. It noted the UK upstream industry was in 2016 expected to approve less than £1 billion to spend on new projects, compared with a typical £8bn per annum over the last five years. And it cited “fears for the long-term future of the industry”.

The likes of Scottish Chambers of Commerce have highlighted the drag on the overall economy north of the Border from the oil and gas sector’s woes.

Clearly, the toiling Scottish economy does not need further damage inflicted on it by uncertainty around EU membership or, far worse, an actual vote to leave the free trade bloc.

At least Scottish businesses have been making their voices heard increasingly in the EU membership debate.

Standard Life has hammered home its belief that the UK should stay in the EU, with chairman Sir Gerry Grimstone and chief executive Keith Skeoch vociferous on this crucial issue when the Edinburgh financial giant unveiled results last week. And Weir Group this week warned of a danger of years of volatility in the event of an EU exit.

Weir Group finance director Jon Stanton, citing the potential impact on the pound as an example, said a vote to leave the EU “could mean there will be volatility in years to come, which we don’t think would be at all helpful”.

Standard Life and Weir Group were both strong supporters of the Union ahead of the September 2014 referendum on Scottish independence.

Asked whether Weir Group had a view on talk that a vote for the UK to leave the EU could trigger a second Scottish independence referendum, Mr Stanton replied: “One at a time is pretty much the view – focused on the EU and see where we get to.”

It is likely some supporters of Scottish independence will be hoping the UK electorate overall votes for Brexit, but that the breakdown of the result will show people in Scotland preferred strongly to stay in the EU.

This might, views on constitutional change aside, seem a bit like needing two results to go the right way for the Scottish national football team to make it to the World Cup or European championships. Or, in the old days, to get through the group stages of the World Cup. Hopes of such combinations of results have often proved forlorn.

But opinion polls are indicating, when it comes to the EU referendum, what some independence supporters likely want in terms of two different results for Scotland and the UK as a whole may well happen.

The debate will go on about the benefits and disadvantages of Scottish independence. The situation prevailing in the oil and gas sector will likely be a key factor but so too, for very good economic reasons, will the position regarding membership of the EU.

In this context, it is worth reiterating an observation from banking giant Citi. In a note warning Brexit could hit the pound and UK economic output significantly, Citi said: “The Scottish electorate might well prefer the uncertainties of independence within the EU to uncertainties of Brexit.”

Whatever transpires on this front, one thing seems clear: an exit from the EU would be bad and possibly calamitous for the Scottish and broader UK economy.