Britain's Home Office has reported a substantial rise in the number of terrorism-related arrests so far in 2015.

Figures released Thursday show 315 arrests on terrorism-related offenses for the first nine months of this year, compared to 235 in the same period in 2014. That represents a 34 percent increase, explained in part by the increasing number of women and teens arrested.

The statistics show that 50 women have been arrested for terrorism-related offenses this year compared to 21 in the same period in 2014.

The number of people under 18 who have been arrested also increased from eight to 15.

Not everyone arrested is charged with a crime.

The British government has said an attack is highly likely and the threat is assessed as severe.