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Jamie Oliver is set to close six of his Italian restaurants across the UK Getty Images

Jamie Oliver has blamed the mounting "pressures and unknowns" that have followed the Brexit referendum for his decision to close six of his Italian restaurants across Britain.

The popular chef's chain said on 6 January that Jamie's Italian restaurant in Ludgate Hill, next to London's St Paul's Cathedral will be closed by the end of the first quarter of this year, along with restaurants of the same chain in Aberdeen, Exeter, Cheltenham, Richmond and Tunbridge Wells.

"As every restuarant owner knows, this is a tough market and post-Brexit the pressures and unknowns have made it even harder," said Simon Blagden, chief executive of the Jamie Oliver Restaurant Group.

"Because we refuse to compromise on the quality and provenance of our ingredients and our commitment to training and developing our staff, we need restaurants that can serve an average of 3,000 covers every week to be sustainable."

He added the restaurants made up less than 5% of the company's total turnover, indicating the company, which boasts 42 sites across the UK, plus an additional 36 abroad, will focus on further expansion outside of Britain.

"In the UK we will be focusing on our core Jamie's Italian estate and on the expansion of the Barbecoa brand which will see two new openings in 2017," he said.

"Internationally we plan to launch another 22 Jamie's Italian restaurants with our current partners and are also looking forward to focusing on running and developing further our newly acquired Australian restaurants."

Approximately 120 employees, amounting to less than 5% of the chain total workforce, are expected to be affected by the decision, although the company has already stated they will be offered a position at other Jamie's Italian restaurants.

"These closures are in no way a reflection on the the dedication and commitment of our staff and my first priority is to try and secure those affected alternative jobs," said Blagden.

"Where this isn't possible, we'll be working with them to find alternative employment."

Despite the planned closures, Blagden remained upbeat over the company's outlook, indicating the chain was in rude health.

"Our overall business is in very good shape, we finished last year with like for like sales growth and an increase in covers,"he said.

"Jamie's Italian has become a much loved presence on the UK high street and we have our teams to thank for that."

In 2015, Jamie's Italian saw profit slump 39% year-on-year to £2.3m, largely due to fees from a failed process aimed at securing private equity support. However, the chain's turnover rose almost 9% £116.1m, making the group the biggest contributor to Oliver's group of companies, whose total revenues rose 2% to £158m with pre-tax profits of £10.2m.