Almost 200 business leaders have set out the case for Britain staying in the European Union, warning of a risk to investment and jobs if the country opts to leave the 28-nation bloc in a national vote this June.

In a letter published Tuesday in The Times, the leaders say business "needs unrestricted access" to the European market in order to grow and invest.

Signatories include CEOs at over a third of the country's biggest businesses, including BP, Burberry and AstraZeneca. Heathrow and Gatwick chiefs also signed.

The bosses of Tesco and Barclays are notable absentees.

The letter was organized with the support of Prime Minister David Cameron's office.

Vote Leave Chief Executive Matthew Elliott says the letter provides further evidence that "panic seems to be spreading" at Cameron's office.