Childline must be given more funding from government, 130 MPs have said in an open letter as the helpline sees demand from suicidal children almost treble.

The NSPCC said its helpline is struggling to cope with a growing number of complex cases, a rising number of which come in overnight as children are more likely to have access to tablets and mobile phones.

It now offers counselling via email, online chat and via a mobile app but struggles to recruit volunteers to work the unsociable hours when children are increasingly likely to call.

Figures from the charity show that the number of sessions for children who are struggling with suicidal thoughts and feelings has risen from 8,835 in 2010-11 to 22,456 in 2016-17, and they now make up almost 10 per cent of the charity's counselling.

Two thirds of counselling sessions about mental and emotional health, self-harm and suicide are now delivered between 5pm and 9am, and one in three counselling sessions about mental health take place over the weekend.

In one in every four cases, calls or contacts go unanswered, the charity said, as not enough counsellors are available.

The growing number of cases which involve suicidal thoughts also mean that volunteers need extra training to help them deal with the more complex issues they throw up.