They are at risk of being bullied, dropping out of school and turning to crime, according to children's communication charity I Can.

The charity published a report, backed by the BT Better World campaign, warning that speech and language difficulties can seriously damage children's life chances.

In some of the more deprived parts of the UK, between 50% and 80% of children start primary school with "delayed language".

This means they may not speak clearly, they may have a smaller vocabulary than normal, use shorter sentences and understand only simple instructions.

Melanie Cross, the report's author, said: "Good speech, language and communication skills equal good life chances. It is that simple.

"Without them, children struggle to interact socially, manage their emotions, negotiate, problem solve and resolve conflict - all of these skills rely heavily on language.

"Equally, we need to make sure that vulnerable people already in 'the system' receive all the help and support they need."

Virginia Beardshaw, I Can chief executive, said children who find language hard "find life hard".

"This report clearly shows that developing children's speech, language and communication skills early is vital and can help children avoid a lifetime of exclusion," she said.