Tens of thousands of British children are having their tonsils removed "unnecessarily", a new study suggests.

Researchers said seven in eight youngsters given the procedure were unlikely to benefit from the operation.

These "unnecessary" procedures are costing the NHS tens of millions of pounds a year, they added.

The most common reason for a tonsillectomy is a recurrent sore throat.

Evidence suggests that the procedure results in modest, short-term reductions in recurrent sore throats in severely affected children, the researchers said.

UK guidelines suggest offering tonsillectomy for children with seven or more documented sore throats over the course of a year, they added.

Researchers from the University of Birmingham analysed health records from more than 1.6 million children from 700 GP surgeries around the UK.

Other "non evidence-based" reasons for youngsters undergoing tonsil removal included obstructive sleep apnoea and other sleep disordered breathing.

They concluded that 32,500 children who undergo a tonsillectomy in the UK each year are "unlikely to benefit" from the procedure.

They said unnecessary tonsillectomies were costing the NHS across the UK £36.9 million each year.

Tom Marshall, professor of public health and primary care at the University of Birmingham, said: "Research shows that children with frequent sore throats usually suffer fewer sore throats over the next year or two.

"In those children with enough documented sore throats, the improvement is slightly quicker after tonsillectomy, which means surgery is justified.

"But research suggests children with fewer sore throats don't benefit enough to justify surgery, because the sore throats tend to go away anyway.

"Our research showed that most children who had their tonsils removed weren't severely enough affected to justify treatment, while on the other hand, most children who were severely enough affected with frequent sore throats did not have their tonsils removed.

"The pattern changed little over the 12-year period.

"Children may be more harmed than helped by a tonsillectomy.

"We found that even among severely affected children, only a tiny minority ever have their tonsils out."