While hundreds of thousands of sixth-formers across Britain anxiously await their A-level results on Thursday, university leaders across the country are waiting just as nervously in what is thought to be the toughest ever student recruitment season.

Britain’s 160 higher education institutions have enjoyed a rising tide of applications from prospective undergraduates, barring a dip in 2012 when tuition fees first rose to £9,000. But this year the tide has gone out – and some vice-chancellors fear they will be left stranded.

Figures from Ucas, the admissions clearing house, have shown a sharp fall in the number of applications for undergraduate study from UK-based students for the first time since 2012, as the shrinking demographic pool of secondary school leavers has combined with fewer applications from mature and part-time students.

In previous years applications from EU and non-EU students have been an area of growth. But now the Brexit referendum and its associated uncertainty has seen a marked decline in EU applications, despite strenuous efforts by the government and the higher education sector to reassure prospective students that they won’t be affected by the turmoil.

“Right now, it feels like musical chairs. Somebody is going to miss their recruitment targets, and nobody wants it to be them,” said the head of admissions of a Midlands university who did not want to be identified.

“It’s the toughest season I can remember. We’ve all got our fingers crossed.”

The competition has been made harder this year by the expansion in numbers being offered by the prestigious universities within the Russell Group of research-intensive institutions, taking students who not long ago would have been looking elsewhere.

The result has been a surge of marketing as budgets have been strained: London Metropolitan University has blanketed some of London’s double-decker buses in bright yellow and its logo, along with tube station turnstile cladding boasting of its graduates’ high employment rates.

Others, such as Leicester’s De Montfort University, have aggressively pushed the university’s recent gold award in the government’s new teaching excellence framework. De Montfort’s management hope that the lustre of gold will help it recruit international students from China, and counteract the stiff competition in its domestic market.

The University of Sheffield – a member of the Russell Group – said it has managed to buck the post-Brexit trend in recruiting EU students. It expects to see an increase in applications from the EU, after putting in extra effort through the networks it has built up around Europe.

However, even among the Russell Group, recruitment remains a top priority. “The challenge that is facing the sector this year is that we’re feeling that demographic dip. There are just fewer 18-year-olds. I think that puts everyone in the sector in a difficult position,” said Christina Edgar, head of student recruitment at Sheffield.

“Ever since the government caps on student numbers were lifted a couple of years ago, institutions have had the choice of how many students they accept on to their courses.

“As soon as that happened, various institutions have made choices about growing a little bit or a lot. That means that when there are fewer 18-year-olds, there is a lot of choice for those 18 year-olds, because we could all potentially take a few more students than we used to.”

As a result, the canny among this year’s cohort of school-leavers are able to leave their choices until the last minute – through the process known as clearing and adjustment – and after they know their A-level results later this week.

“It means that if a student wants to take a fresh look in August, or has changed their mind about what course they want to do or what part of the world or what part of the country they want to be in, they’ve got the choice to do that.

“I think they are just more aware of that, they are more aware that it is their decision,” said Edgar.

Like an increasing number of universities, Sheffield catered to late deciders by offering campus tours and open days for prospective students and their families in the weeks leading up to A-level results day – and is even hosting campus events in the days after results are published.

Marketing too increasing takes places online. Google’s paid ad search rankings show Aberdeen, Huddersfield and Roehampton universities paying for top search result spots alongside private providers such as the New College for the Humanities.

Meanwhile, on social media, university recruitment now uses the full range – with an emphasis on Facebook Live and Snapchat this year – to make initial contact with students.

Some, such as Staffordshire University, are even prepared to make offers to students via Snapchat, Facebook and Twitter during clearing, with “in principle” offers followed up via the normal admissions process.

“We know that results day is an agonising time for some and young people can feel extremely anxious about picking up the phone and making the call,” said Clare Beckett, Staffordshire’s director of student admissions.

Nick Hillman, director of the Higher Education Policy Institute, said that the removal of student number controls on individual institutions since 2012 was welcomed by the more ambitious universities.

“The old situation was really strange. You had willing students and willing universities, and they weren’t allowed to matchmake with each other,” said Hillman.

Hillman thinks the fall in applications – especially in nursing, which has suffered the biggest drop in interest since the government replaced student bursaries with loans – may not be as negative as the initial data suggests, if it is the more marginal candidates who have been put off.

Among those school-leavers in England receiving their A-level results later this week, appetite for full-time study has never been stronger.

Ucas’s data showed that the proportion of the 18-year-old population in England applying has increased from 37.2% last year to 37.9% in 2017, the highest level on record – despite tuition fee increases to £9,250 a year and the prospect of graduating with student loan debt averaging more than £40,000.

But Gordon Marsden, Labour’s shadow minister for higher education, said the figures mask how much the burden of costs is being passed to future students through higher student loan costs and the scrapping of maintenance grants.

“If you then throw in the disastrous fall in the numbers of part-time and mature students – on which the government so far has only offered derisory initiatives, too little, too late – you get a sense of how the nudge factor so beloved of Tory theorists is now working to push would-be students away from higher education, not towards it,” Marsden said.

Marsden’s comments were supported by new figures from a Sutton Trust survey showing that the proportion of schoolchildren who are aiming to go to university has fallen to its lowest level in eight years.