51�Թ�

"The investigation is still in its early stages and we are exploring various lines of enquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter," said Cdr Dominic Murphy, head of the Met's counter-terrorism command.

HMS Alban's commanding officer, Cdr Matt Teare, said the "regularity of Russian activity around the United Kingdom reinforces the vital importance of continuous integration with our allies and partners".

Cdr Teare said the frigate "is at very high readiness to operate whenever, and wherever, the nation needs us in the protection of our home and the waters surrounding it".

Cdr Kevin Southworth - who leads public protection at the Metropolitan Police - told the BBC officers were still working their way through the 23 potential new cases and that some of the people were "definitely not identical" to those featured in Zou's seized secret footage or from the charge cases for far.

"We want to avoid situations where victims feel like they're maybe not being taken seriously, or heaven forbid, being disbelieved," says Cdr Southworth.