A late plea for voters to back the remain option in this week’s EU referendum has been issued by 1,285 business leaders who say in a letter to The Times that Brexit would damage Britain’s economy.

Smaller businesses and employers would be particularly vulnerable to any economic shock as a result of a leave vote, according to its signatories, who include the leaders of 50 of the FTSE 100 companies.

“Britain leaving the EU would mean uncertainty for our firms, less trade with Europe and fewer jobs,” they say in the letter.

The letter goes on to claim that the terms of trade between Britain and its European market would have to be reset “from scratch” in the event of a Brexit.

Its signatories included the founder of the Virgin Group, Sir Richard Branson, who this week launched his own nationwide campaign to urge people to back remain, and Michael Bloomberg, the former New York mayor, who has already claimed that a vote for Brexit could lead to job losses in Britain and harm its ability to fight terrorism.

They were joined by Jo Malone, the perfume entrepreneur, and Charles Dunstone, the co-founder of Carphone Warehouse.

Figures from a number of FTSE 100 companies who had previously not added their voice to calls earlier this year also signed the letter. They included leaders from the ranks of Barclays, Anglo American, Standard Life, Barratt Developments and the Berkeley Group.

While major institutions are represented in the letter’s list of signatories, it says of a potential Brexit: “Smaller businesses and the people they employ are particularly vulnerable to any economic shock which could follow.”

Boris Johnson, one of the most prominent Tory figures in the Vote Leave campaign, said on Monday that Downing Street was waging an operation to pressurise business leaders into supporting the remain side.