The number of Islamism-inspired terrorism offences in the UK has nearly doubled in the five years to the end of 2015, according to a new report.
The period from 1998 to 2015, studied in a report on Islamist terrorism on British soil, has also seen a surge in the number of women taking part in these crimes with offenders are getting younger and the bulk of the Islamism-inspired threat coming from home-grown terrorism.
It was found that 72% of Islamism-related offences (IROs) were carried out by UK nationals or people who held dual British nationality.
Report author Hannah Stuart, a fellow at The Henry Jackson Society who commissioned the study, believes it poses particular challenges for the authorities.
She said: Our security services will be particularly concerned that the major threat continues to be home grown and that females are playing an ever increasing role in terrorism.
Such a high concentration of offenders in London and Birmingham will also focus the minds of policy makers when it comes to deciding where to target our counter-terrorism efforts.
There were 269 individual offences and 264 convictions for Islamism-inspired terrorism offences as a result of arrests from 1998 involving 253 British or foreign nationals.
Looking at all 269 offences, researchers found the number of IROs had nearly doubled in the five years to 2015 from 12 to 23 per year while the amount of all terrorism cases had risen from five per year between 1998 to 2010 to 14 per year between 2011 and 2015.
Women accounted for 4% of IROs between 1998 and 2010 but 11% between 2011 and 2015.
The report states: Eighteen women have been convicted of terrorism offences ranging from supportive offences such as assisting an offender to serious attack-related offences such as attempted murder.
More than half of the female cases involved behaviour that was supportive of men with whom they have a family or personal relationship, or was accepted by the trial judge as subordinate to that of their partner and co-accused.
British terrorists are getting younger, according to the report, as 46% of the 2011-2015 offences were carried out by people who were aged under 25, up from 42% for offences committed between 1998-2010.
The most common age for an Islamic terrorist was 22, a third of women offenders were 22 and the average age overall was 26.8 years old.
In general those who carried out terror attacks were aged between 14 to 52 years old.
Among all the offenders, 72% counted London, the West Midlands or North West England as their home. No other region contained 10% of residences, the study found.
London was where 43% of terrorists lived when they were arrested for an IRO.
The second most common region was the West Midlands where 18% of offenders lived, and the bulk of these people came from Birmingham.
The third biggest hotspot was North West England with 10% of IROs.
East London was home to 50% of London-based offenders, who mostly came from the boroughs of Tower Hamlets, Newham and Waltham Forest.
The report also states that 48% of English-based IROs were committed by people living in the most deprived 20% of neighbourhoods nationally, commonly referred to as highly deprived’.
In a general overview researchers found that 52% of offenders had Southern Asian backgrounds and were most commonly British Pakistani.
There were 76% who were already known to authorities when they committed their offence and 26% of offenders had a previous criminal conviction.
Ms Stuart said: As we continue to improve our policing of Islamism-inspired terrorism the prevalent national security threat of our age we should be aware that the vast majority of UK-based terrorists do not act alone.
This research shows that the overwhelming majority are part of wider networks, formed online and in person, with family and friends and most have been radicalised here in the UK.