UK-based tour operator Thomas Cook has lost its place in the FTSE 250 of leading shares.

The troubled operated will drop to the FTSE Small Cap index.

The quarterly review used the closing prices from Tuesday, with the changes confirmed by a FTSE committee on Wednesday.

The index changes will be implemented from the start of business on December 19th.

Earlier Thomas Cook said it will announce its delayed preliminary results for the 12 months ended 30th September 2011 on Wednesday December 14th – more than three weeks later than expected.

At the same time the brand will reveal the results of the UK business review.

Shares in Thomas Cook nosedived last month after the tour operator confirmed it was in talks with banks to secure additional credit to ensure survival over the slow winter trading.