Thomas Cook Group has warned it is at risk of insolvency and is reportedly in talks to increase the size of a rescue package to £1 billion.

Sky News reports that Thomas Cook is seeking an extra £100 million from lenders, on top of the £900m already proposed.

It operates from Glasgow, Edinburgh, Aberdeen and Prestwick.

Sky News said that in a court filing dated August 30 Thomas Cook warned that it was running out of time to secure its future.

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The legal memo, which asked the courts to accelerate the process for refinancing, stated: "The serious liquidity issues within the group have led to an urgent need to complete any restructuring within September.

"[Any] delay would make it impossible to implement a restructuring transaction within September, and the Scheme Companies would be likely to run out of money and enter into formal insolvency proceedings."

In its most recent stock market announcement about the restructuring on August 28, Thomas Cook referred to an "implementation commitment targeted for early October 2019".

The 178 year old travel agent employs around with 21,000 people, including 9000 in the UK.

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In May, Thomas Cook reported a £1.5bn loss for the first half of its financial year, with £1.1bn of the loss caused by the decision to write down the value of My Travel, the business it merged with in 2007.

It also put its airline up for sale to raise cash.

It has blamed factors including holidaymakers delaying travel due to Brexit, and the unusually hot summer in 2018 for some of its financial challenges.

However, it is also under pressure from changing trends, including a growth in online travel agents and people increasingly putting together their own trips.