 Police officers conducted a series of raids in London on Friday |
It follows a series of raids carried out since the bombing, ending in an armed swoop in west London.
Metropolitan Police Commissioner Sir Ian Blair told BBC Newsnight the attacks and subsequent investigation would "reshape British policing".
Despite the fast-pace of raids and arrests, he said the force would need to look at what effect terrorism would have on policing.
"Can we do all of this mission if this is going this way? And if we can, then what's the sort of additional costs that are required?" he said.
'Largest investigation'
Two weeks on from the July 7 bomb attacks on the London transport system, in which 56 people, including four bombers, were killed and another 700 injured, another four men attempted a similar attack.
The would-be bombers targeted Tube trains at Oval, Warren Street and Shepherd's Bush Underground stations and a number 26 bus in Bethnal Green.
All four of the bomb suspects are now reported to be in custody, after the arrests in London and one in Rome on Friday
The manhunt that followed the attempts was described by Sir Ian as "the largest ever investigation that the Met has ever mounted", with officers hunting suspects both in the UK and abroad.
Some 15,000 CCTV tapes have been studied by officers, along with 1,800 witness statements and more than 5,000 calls to the anti-terror hotline.
The first significant police action following the attempted bombing resulted in the death of an innocent man.
Brazilian national Jean Charles de Menezes, who was working in London as an electrician, was shot dead by police at Stockwell station, south London, on the morning of Friday July 22.
 Sir Ian Blair called for more 'good old fashioned detective work' |
A subsequent series of raids were carried out across the capital, resulting in the discovery of possible explosives in a car at East Finchley.
A package found in bushes at Little Wormwood Scrubs in north-west London was also believed to be linked to the attacks, with speculation that a fifth bomber may have abandoned plans at the last minute.
The release of CCTV images of the four suspects along with the names of two of the would-be bombers prompted more than 500 calls and e-mails to police, aiding the inquiry.
Taser gun arrest
Another break came on Wednesday when police arrested four men at two addresses in Birmingham.
One of the men, who was shot with a Taser stun gun, was named as Yasin Hassan Omar, wanted as a suspect in the Warren Street attempted bombing.
On the same day, three women were also arrested at Blair House, 200 yards from Stockwell Tube station in south London, on suspicion of harbouring offenders.
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 It's detective work, we actually need, this is good old, old fashioned detective leg work.  Sir Ian Blair |
On Friday police carried out a series of raids in the Notting Hill area, resulting in the arrest of three men, two of which are believed to be the July 21 bombers.
They are Muktar Said Ibrahim - suspected of trying to bomb a bus in Shoreditch - and a man, who police have not yet named, wanted over the attempted Oval Tube bombing.
Despite the quick pace of developments, Sir Ian said British policing is facing difficulties in tackling terror attacks.
"I think there has to be a substantial increase in three fields really," he told Newsnight.
"It's detective work, we actually need, this is good old, old fashioned detective leg work.
"We need firearms capability. We've got enough firearms officers but not enough to do this length of tour, as it were.
"People have to have rest. They can't, you know, they can't just keep carrying a gun hour after hour, day after day.
"And then thirdly it's around the forensics and explosive capability or rather counter-explosive activity.
"So in other words we're pushing at the specialist areas and that is a difficulty for us".
BBC security correspondent Frank Gardner said that despite arrests the investigators will still want to know who planned the attacks, who recruited the 7 July suicide bombers and the attackers of 21 July and where could they be hiding.
There were also fears that an unknown terror cell could still be at large in Britain, he added.