The UK risks an exodus of talent from its creative sector, leading arts organisations and industry bodies have warned, as they call on the chancellor to extend financial support for freelancers until 2021.

Indoor live performances in England were given the green light from 15 August as part of the easing of Covid-19 restrictions. However, professional body the Incorporated Society of Musicians, and performing arts union Equity, fear venues will struggle to reopen because smaller audiences mean less profit from ticket sales.

They are asking for the Treasury’s self-employment income support scheme (SEISS), which in its second round will award individual grants of up to £6,570, to run until spring 2021 – far beyond its current cut-off date of 19 October.

The Brit School, UK Theatre, the Society of London Theatre, the Glyndebourne Tour Orchestra and the London Symphony Orchestra are among the high profile signatories to the letter sent to the chancellor, Rishi Sunak.

Paul Fleming, the general secretary-elect of Equity, which has 48,000 members, said: “Equity’s members are heading toward a cliff edge with a parachute full of holes.

“The SEISS excluded some of the lowest paid and most under-represented self-employed artists from the beginning, and now it’s going to be ripped away from even those who were covered.

“Unless the government introduces meaningful income support for our members until reopening and beyond, we’ll barely have a workforce left.”

Deborah Annetts, the chief executive of the Incorporated Society of Musicians, welcomed venues being allowed to reopen live performances but said that many could not afford to stage shows because social distancing. She believes this will mean little work for freelancers until 2021 with many creatives forced to leave the profession.

“Without a financial intervention of this kind, the government risks the loss of the talent which makes the creative industries so successful in this country and generates £111bn for the economy each year,” she said.

The letter to Sunak described a likely “exodus of talent” from the creative sector and a sudden decline without continued financial support.

The government has described its second self-employed worker grant scheme as its final payout.

So far in England, 2.2m claims were made when the first grants were available, totalling £6.4bn .

Other support for self-employed people includes the government’s Bounce Back Loan scheme, income tax deferrals, increased levels of universal credit and mortgage holidays.

A government spokesperson said: “We are doing everything we can to support the arts sector during this crisis. Around 75,000 people who work in the arts have received more than £200m in government grants though our self-employment support scheme – with a second payment now available to those in need.

“This is in addition to a historic £1.57bn support package for UK culture to help the hardest hit organisations through the crisis and protect the jobs they provide, ensuring work continues to flow to freelancers.”