Britain's financial watchdog has opened an investigation into infrastructure giant Carillion as the troubled firm's woes continue.

The UK company, which is embroiled in an ongoing crisis that has involved a string of profits warnings, said today the Financial Conduct Authority (FCA) is probing the "timeliness and content" of announcements made between December 7 2016 and July 10 2017.

It covers a period of turmoil for the HS2 contractor, in which  the firm's share price plunged and its chief executive departed following a warning over profits.

Carillion said it is co-operating fully with the FCA.

In December, the firm, which is scrambling to reduce its debt pile, struck an agreement with its lenders to defer a crucial financial covenant test, a development that will give the troubled group more breathing space.

In November, the HS2 contractor issued its latest profit warning and said it will breach its debt covenants, which resulted in another share price collapse.

The firm said at the time that annual profits are set to be "materially lower than current market expectations" as it grapples with a string of delays and smaller-than-expected improvements to margins on certain contracts.