Banking firm Revolut analysed the data of its 6,000 customers in Sheffield between May 17 – when indoor hospitality resumed – and June 13.
Sheffield punters spent 64% more in pubs over this period than they did compared to the previous month – when only outdoor hospitality was allowed.
But spending was still 66% below the level recorded in February 2020, before the pandemic struck.
Across Great Britain, spending in the month since pubs reopened their doors for indoor service was still 58% lower than in February last year.
Mr Johnson pushed back the end of England’s coronavirus restrictions to July 19 due to concerns over the rapidly spreading Delta variant first identified in India.
Pubs across the country had been preparing to welcome customers back with no limits on social contact or group sizes from Monday (June 21).
Sector leaders including the British Beer and Pub Association, UK Hospitality and the Campaign for Real Ale say they are “bitterly disappointed” by the delay, which they estimate will cost pubs £400 million alone.
A joint spokesman said: “Our sector is facing one of its toughest periods in its history and this latest delay is yet another setback.
“Many pubs cannot break even under current restrictions and around 2,300 still remain closed
“It is now absolutely critical that the Government provides our sector with further support – else the recovery of our pubs will be over before they’ve even been given a chance.”
They have also called on the Prime Minister to prioritise the additional £1.5 billion business rates support package announced back in March, to ensure eligible businesses such as brewers can apply as soon as possible.
Revolut figures also show that spending in restaurants across Britain was still 51% below normal in the four weeks to June 13.
In Sheffield, it was 52% below the pre-pandemic baseline.
Experts feared going ahead with step four could lead to hospital admissions on the scale of the first wave of Covid-19, heaping unsustainable pressure on the health service.
Limits on numbers for pubs and restaurants will therefore remain in place and nightclubs will stay shuttered.
Mr Johnson left open the option of ending restrictions on July 5 if the data proves drastically better than expected, but conceded “let’s be realistic, probably more likely four weeks”.
He added: “It’s unmistakably clear that vaccines are working, and the sheer scale of the vaccine roll-out has made our position incomparably better than in previous waves.
“But now is the time to ease off the accelerator because by being cautious now we have the chance in the next four weeks to save many thousands of lives by vaccinating millions more people.”
Separate figures from the Office for National Statistics also show that UK pubs had been under increasing pressure before the pandemic even began.
The number of pubs fell to 38,900 in March last year – down slightly from 2019, and significantly fewer than the 52,500 in 2001.
In Sheffield, this figure fell from 465 in 2001 to 330 in 2020.