The main ingredient in the 7/7 bombs is easier to buy than large numbers of aspirin pills, the coroner at the inquests into the attacks has said.
Lady Justice Hallett said significant quantities of hydrogen peroxide could still be bought without much risk.
Photographs have been released from a bomb factory in Leeds showing the explosives and chemicals used to make the homemade devices used on 7/7.
Four suicide bombers killed 52 Tube and bus passengers in the 2005 atrocity.
Lady Justice Hallett told the inquests at the Royal Courts of Justice in London: "So you get cross-examined by the chemist if you want to buy too many aspirin, but you can buy as much hydrogen peroxide on the market."
The court heard that although the four bombers bought large amounts of the chemical in the months before the attacks, none of the sellers alerted police with any concerns.
The barrister representing four of the bereaved families, Gareth Patterson, said: "It is clear, isn't it, that in making these purchases the four men didn't act to any great degree in a covert way.
"They simply found these places, often using the internet, drove there, purchased the liquid oxygen and left."
Dc Richard Reynolds, of the Metropolitan Police's SO15 counter-terrorism command, answered "Yes".
Photographs showing the explosives and chemicals used to make the homemade devices were released at the inquest.
A bath full of chemicals and pans used to boil hydrogen peroxide were among the images from the bomb factory at 18 Alexandra Grove in Leeds.
A police raid at the address five days after the London bombings uncovered high explosive, a detonator, respirators, and other items.
Hot plates connected to fans used to concentrate the hydrogen peroxide were found throughout the two-bedroom flat, the inquest was told.
One of the bedrooms contained plastic tubs holding a yellow-brown explosive sludge, while the lounge was strewn with packaging from items bought for the devices.
The bombers also taped curtains to the walls to screen themselves from the outside world.
Dc Richard Reynolds, of the Metropolitan Police's SO15 counter-terrorism command, said many of the items found had an innocent everyday use but were "significant" in the context of the inquiry.
The detonator was made from the explosive HMTD, but also a light bulb, wire, and aluminium foil, the inquest heard.
Bombers Mohammad Sidique Khan, 30, Shehzad Tanweer, 22, Jermaine Lindsay, 19, and Hasib Hussain, 18, made no attempt to disguise their work, the court heard.
Dc Reynolds said: "The environment that they are working in would have been quite hostile... within the actual premises itself, nothing was actually secreted or hidden."
The bombers used respirators because the hydrogen peroxide gave off noxious fumes as it was boiled down, blistering paint work and killing plants outside one of the ground-floor flat's windows.
Dc Reynolds said there would have potentially been an unusual smell near the open window, which he would have investigated had he smelt it.
The inquest was also shown images of smaller bombs found in the Nissan Micra used by three of the bombers to get from Leeds to Luton station on 7/7.
The devices were covered in nails and might have been used to throw at the police if they were caught, the hearing at the Royal Courts of Justice in London was told.
The main bombs used in the attacks on the number 30 bus and Tubes at Aldgate, Edgware Road and Russell Square, contained about 10kg (22lb) of explosives made from hydrogen peroxide and pepper, and detonated by a 9-volt battery.
Forensic explosives expert Clifford Todd said the combination of materials was unique in the UK and worldwide.
He said the four terrorists would have needed outside help to make the bombs and suggested no attempt was made to hide their identities as intact identification was found at all four bomb sites.