Sadiq Khan has claimed the Government is "pulling the curtain down" on the capital's creative industries, in a call for more funding from Ministers.
The Mayor's warning comes as a new City Hall report reveals that 25 per cent of London's arts organisations could lose funding and 10 per cent could leave the city altogether.
The Department for Culture, Media and Sport (DCMS) said London receives a third of national spending by Arts Council England (ACE) - significantly bigger than its population size relative to the rest of the country.
City Hall's report warns that ACE, which is an arms-length body of DCMS, is "implementing a significant and potentially damaging restructuring" of its portfolio of London-based organisations.
It says that of those affected, a quarter of funded organisations (66 out of 268) in London will lose grant funding with "a threat to their viability", while another 10 per cent of organisations (24) will have to leave London to retain funding.
The English National Opera (ENO) is perhaps the most prominent organisation which has been told it will have to leave London to retain its funding.
"London's culture and creative industries are the envy of the world and a huge driver of the UK's economy, and it is vital that they are properly funded," said Mr Khan.
"Instead, these organisations are facing unsustainable gaps in resource while dealing with spiralling operational costs, soaring energy bills, Brexit bureaucracy, and the ongoing impact of the pandemic.
"Pulling the curtain down on London's cultural offering is not going to help shine a spotlight on other towns and cities.
"These funding decisions will have lasting social and economic consequences and I am urging Ministers to ensure that meaningful support is made available nationwide."
A DCMS spokeswoman responded: "London receives a third of the national spending by the Arts Council, which is reflective of the capital's reputation for having one of the best cultural offerings in the world.
"Arts Council England's investment is supporting many of London's internationally renowned institutions while also spreading funding more evenly across the city's boroughs, bringing more culture to the doorsteps of millions.
"Theatres, orchestras, museums and galleries also benefit from generous tax reliefs."
Earlier this month, protesters from the performing arts union Equity attended a meeting of the London Assembly, as it unanimously passed a motion calling on the ENO to be allowed to keep its primary base in the capital.
Commenting specifically on the planned re-location of the ENO, a spokeswoman for ACE responded to that motion: "As a condition of receiving a 2 per cent increase to our budget at the 2021 spending review, we were instructed by government in February 2022 to move £24m a year out of the London portfolio of funded organisations by 2025, and spread funding in the capital to more boroughs.
"Change in how we invested in London was inevitable, and with the budget available to us we had to make difficult decisions between good applications to support all types of cultural work and make sure the spread of this public investment was reaching more people, in more places.
"We understand there is a challenging period of transition for the company and its staff and have invested £11.46 million to support the English National Opera (ENO) in 2023-24.
"In addition up to £24 million is available to the ENO for 2024-26 to support a phased transition to a new artistic and business model, and will include work split between their new primary base and the London Coliseum."
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