IT has seemed from day one of the Brexit campaign that many of the supporters of this entirely damaging odyssey have failed to grasp the reality that the British Empire has gone for good.

The UK, economically, is not an insignificant force on the global stage but its influence has been waning, and the Johnson administration’s ripping of the country from the world’s largest free trade bloc has at the very least made it an international curiosity. Some have declared that Johnson and co.’s hard Brexit has made the UK a laughing stock on the global stage, and it is easy to see why they have come to this conclusion.

There has been a huge drive by the UK Government to try to ramp up trade with Commonwealth countries post-Brexit, as it has seemed to take an “anyone but EU” approach on this front.

It has on occasion been truly excruciating to watch.

And you wonder at times whether the leaders of those countries with which the UK has been chasing more trade might have been somewhat surprised at the degree of enthusiasm shown by Prime Minister Boris Johnson and other Cabinet members in their wooing.

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Mr Johnson made a high-profile visit to India last week – which generated memorable pictures and video of him being fitted with a turban – and a free trade agreement with this populous Asian country looked to be right at the top of his agenda.

The Prime Minister emphasised in no uncertain terms his desire to conclude a free trade deal by Diwali in October. India’s Prime Minister, Narendra Modi, talked about the end of the year.

It is not the biggest time difference in the world but it appeared to enhance what looked like an already clear picture that the UK was the keener of the two partners. There have been many occasions on which the UK Government has seemed to exude desperation in its endeavours on the global stage – the type of behaviour which were it to be displayed on a first date might send the other party running a mile.

After waxing lyrical about business tie-ups between the UK and India, including in electric buses, robotic surgery and artificial intelligence, Mr Johnson declared during his visit last week: “And perhaps most significantly for the long term, we are making full use of the freedom that we now have to reach a free trade agreement, a deal where you can lift those tariffs – you can, India, Narendra, on our machinery and apples – actually you’ve already done it on apples so thank you for the apples, and we in turn, we can lift the tariffs on your rice and textiles.

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“We’ve already closed four chapters, and today we’re announcing new measures to make it easier to export UK-made medical devices to India and ensure mutual recognition of UK higher education qualifications.”

And, looking forward to the next round of talks this week, Mr Johnson added last Friday: “And as the next round of talks begins here next week, we are telling our negotiators: get it done by Diwali in October. Get it done by Diwali.”

Continuing his enthusiastic outpouring, he declared: “This could double our trade and investment by the end of the decade.”

Mr Modi said there had been “good progress” and flagged full efforts to conclude the free trade agreement “by the end of this year”.

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This seemed a little bit more measured than Mr Johnson’s exuberance on the subject.

The Johnson administration issued a UK-India “joint statement”, entitled “Towards shared security and prosperity through national resilience”.

This declared: “The leaders welcomed the strong resilience shown by [the] economies of India and the UK and the positive growth in bilateral trade showcasing the potential to double trade by 2030, as envisaged in the Roadmap 2030. They expressed satisfaction at the progress made under the Enhanced Trade Partnership (ETP) and called for early resolution of all pending market access issues in a balanced manner. They looked forward to finalising the mutual recognition of qualifications and a framework for nursing staff and agreed to continue cooperation on outstanding areas related to social security arrangements and legal services.”

Given the rambunctious tone from Mr Johnson as he talked about doubling trade with India, you can understand why some Brexiters might get pumped up about all this. And they would seem unlikely to dwell on the “all pending market access issues” reference to the hurdles to be overcome.

However, it is important always with Mr Johnson and his Cabinet to look at the cold numbers behind the big, exuberant talk.

And, of course, it would be remiss not to compare what the UK hopes to gain through its much-vaunted new trade deals with the losses arising from Brexit.

This is a fascinating comparison.

The benefits the Johnson administration sees from the deal it is pursuing with Mr Modi are set out in a document published in January, entitled “UK-India Free Trade Agreement: The UK’s Strategic Approach”.

This document states: “The estimates point to a long run increase in UK GDP equivalent to £3.3 billion in 2035, up to £6.2 billion in 2035, depending on the depth of the agreement. This relates to a modelled increase in UK GDP of between 0.12% and 0.22%, and is applied to projected GDP in 2035 (around 15 years from the implementation of the agreement).”

So how does this compare with the Theresa May government’s forecasts of the negative impact on UK GDP of Brexit?

The May government forecasts showed Brexit would, with an average free trade deal with the EU, result in UK GDP in 15 years’ time being 4.9% lower than if the country had stayed in the bloc if there were no change to migration arrangements. Or 6.7% worse on the basis of zero net inflow of workers from European Economic Area countries. The Johnson administration has clamped down dramatically on immigration from other European countries.

For all the tub-thumping of the Brexiters, the cold numbers rather put things into perspective, as they also did for the trade deals with Australia and New Zealand offering tiny benefits relative to the huge losses for the UK from leaving the EU.