Business leaders have warned that the government’s plans for a major global investment summit are in danger of falling flat, amid growing frustrations over high costs of involvement and its timing two weeks before the budget.

As a central plank in Labour’s proposals to drive up investment in Britain, the party pledged in the general election campaign to host the summit within the first 100 days of winning power to show that the UK would be “open for business” under a new government.

The event was confirmed last month by the chancellor, Rachel Reeves, and the business secretary, Jonathan Reynolds, for 14 October as a flagship opportunity for up to 300 senior business figures hosted by the prime minister.

However, several business leaders at Labour’s annual conference in Liverpool this week said it was at risk of failing to live up to its high-profile billing, because it would take place while ministers were still thrashing out the details of several major economic decisions before the 30 October budget.

“It’s the wrong way round,” said Stephen Phipson, the chief executive of Make UK, which represents 20,000 manufacturing firms across the country. “There is a concern about the timing, coming two weeks before the budget.

“People will want to know what the government’s priorities are before committing investment.”

One industry source said the government had only started to approach companies within the past two weeks about the event, expected to take place at a central London location – a hurried timescale for a major summit – with proposals to charge up to £250,000 for sponsorship.

While questions remained over several economic priorities, they said the investment summit, as it was described to them by officials, could amount to spending “hundreds of thousands of pounds for a photo opportunity” with Keir Starmer or King Charles.

Government sources did not deny sponsorship costs, but insisted attendance was free of charge.

Another industry source said company chairs and chief executives were unlikely to attend, with several large firms planning to send more junior representatives – including several large Wall Street banks.

Government sources insisted they were having no problems in attracting senior figures, saying “hundreds of CEOs” were flying in from around the world, and that attendance was being strictly limited. Reynolds told bosses on Monday he was struggling to manage overwhelming demand.

It emerged last week that Larry Fink, the chief executive and chair of BlackRock, was being lined up to attend, according to Sky News, as the party battled suggestions it would struggle to attract the 300 industry leaders it had pledged.

Speaking at Labour’s £3,000-a-head “business day”, taking place alongside its main conference, Reynolds said: “The problem is not getting people to come, it’s managing the interest. It’s like planning a wedding.”

It is understood some ministers have privately questioned the summit’s timing, because companies were still awaiting clarity on tax and spending priorities due in the budget. Business surveys this week show uncertainty over the budget is weighing on Britain’s economy, amid criticism that Reeves’ warning of the need for “tough” decisions was hitting confidence.

However, it is thought it would be too late to change course, having promised the summit would form an important role in the government’s first 100 days. The City minister, Tulip Siddiq, said at a fringe event that the timing was in part due to the impact of the snap election on government schedules.

Labour sources also confirmed the government would not be ready to announce its industrial strategy ahead of the summit – a policy which business chiefs have said will be important for steering investment in the economy.

It is understood a green paper will be published alongside the budget to consult on its proposals, before a full launch of the final plan early next year.

A chair of the industrial strategy council, which is expected to oversee the policy, has yet to be appointed, amid reports that ITV chief executive Carolyn McCall had snubbed the opportunity. The government is also yet to appoint an investment minister to coordinate business decisions with government.

Make UK’s Phipson said companies needed clarity. “Key appointments remain unannounced,” he said. “For business to feel truly secure to make those longer term investments, meat on the bones of the industrial strategy must be a priority which comes at speed.”

Jonny Haseldine, policy manager at the British Chambers of Commerce, said the summit would still send an “important signal” that the UK was open for business, and that bosses could take the lead from Labour’s outline commitments on tax.

“The direction of travel from government is encouraging. But businesses, both in the UK and overseas, will be keen to see more detail on competitive planning and tax policies, in order to achieve much needed growth,” he said.

Chris Hayward, policy chair of the City of London Corporation, said the summit would be an important event to sell Britain to the world. However, he cautioned that ahead of the budget, a long-term global tax regime was required.

“Tax is an important part of the equation: it’s no good being in sell mode then around the world people say: ‘Your tax rates are too high.’ The government cannot resolve that immediately but it can set out a pathway, a course of action that will get us to a globally competitive position on business taxes.”

A Labour spokesperson said: “This government has hit the ground running, delivering the change the business leaders were crying out for including major planning reforms, action on late payments and setting up GB Energy. The urgent work of turning around our economy has begun and there is no time to waste on attracting investment to Britain, that is why we have committed to holding this summit in the first 100 days.

“We are on track to deliver an ambitious programme bringing together hundreds of attenders representing the best of business from across the globe.”