A former police chief last week warned that online anti-Muslim sentiment had been "relentless" after the London Bridge attack that killed eight.

Mak Chishty, an ex-Metropolitan Police commander who had been the country's most senior Muslim officer before his retirement, said: "The backlash has been something of a different scale."

Extremists were hoping to “feed off the tension” caused by Islamist terrorist attacks to plot violence of their own, the Government’s independent terror law watchdog warned earlier this year.

David Anderson QC, said in February: “The threat from extreme Right-wing terrorism in the UK is currently fragmented but the massacre perpetrated by Anders Breivik in Norway is a warning against underestimating the threat.

“Both the Government and the courts treat the threat with the seriousness it deserves. Extreme Right-wing ideology can be just as murderous as its Islamist equivalent. A sophisticated network is not a prerequisite for mass slaughter.”

A quarter of those referred to the Government’s Channel programme, which seeks to protect those vulnerable of being radicalised, are now singled out for suspected far-Right extremism.

The increase in far-Right arrests has contributed to a jump in the proportion of white suspects being held under counter-terrorism legislation.

In the year to the end of March, there were 113 arrests of white people, compared with 68 in the year before - an increase of 66 per cent.