Lord Carlile, who was appointed by the government to review anti-terror laws, said: "Further suicide bombings in the UK must be expected, and the targets are unpredictable."
Carlile reported that he had drawn those conclusions after reading government documents that he found alarming.
Four suicide bombers killed themselves and 52 commuters when they blew up three London Tube trains and a double-decker bus on 7 July last year.
Carlile's report came as Tony Blair's government said it was seeking renewal of the power to put restrictive orders on terrorism suspects without charge or trial.
After a debate in parliament last year, the law giving courts the authority to impose restrictions such as house arrest in cases where a terror suspect cannot be brought to trial was passed with the requirement that it be renewed every year.
"Further suicide bombings in the UK must be expected, and the targets are unpredictable"
Charles Clarke, the home secretary, said the country's top law enforcement official told the House of Commons that the government wanted the powers extended. Parliament will probably debate the issue within weeks.
He also said the government would seek to combine several existing anti-terrorism laws into one bill, which it plans to propose to MPs next year.
Carlile, reporting on the implementation of the so-called "control orders", said Clarke had made fair decisions in every case where an order had been imposed on a terrorism suspect. The decisions are reviewed by judges.
Carlile urged authorities to continue investigating those subject to the orders to try to gather enough evidence to prosecute them instead of imposing electronic tags and communications restrictions under the new powers.
Courts can impose a huge variety of restrictions under the powers, including banning suspects from meeting certain people or going to certain places and imposing surveillance on them.
Amnesty International urged against using the threat of terrorism to justify measures that undermine human rights.
It reiterated its opposition to orders that circumvent normal legal procedures to deprive suspects of liberty.
"The use of control orders flies in the face of human rights law which states that people should only be punished if they have been charged and convicted after a fair trial," the group said.
Carlile said 18 orders had been issued since the law was passed, half of which were still in force. Those who were subject to the orders had been previously imprisoned indefinitely without charge or trial under a law that was overturned by Britain's highest court.
Carlile suggested that some of those now detained awaiting deportation should be released on control orders. Britain is negotiating with some Middle Eastern and north African countries with poor human rights records to secure promises that any detainee deported there will be treated humanely.
Charles Clarke wants
anti-terror laws combined
London has reached deals with Lebanon, Libya and Jordan and is seeking others.
"I have a real concern about the detention under deportation procedures ... of persons who in practice cannot be deported at present and are unlikely to be capable of legally compliant deportation within a reasonable time," he said.
However, he hit back at critics who have said the agreements are meaningless because Britain could not enforce the promises made in them.
"It really is a counsel of despair to suggest that no verifiable or satisfactory agreements can ever be reached with apparently recalcitrant countries," Carlile said.