US pay for the killing of his dead boss, Taliban chiefs revealed on Saturday. He is ordering his followers to 'crush' the city.
Soon after being officially appointed caretaker chief of the terrorist group, Adel vowed to avenge the death of his former boss, the Daily Mail reported.
"Our new leader has asked for a big plan for London," Taliban spokesman Ehsanullah Ehsan said.
"He believes the UK is the backbone of Europe and must be crushed."
A poster released by the FBI shows a photo of Saif al-Adel, one of America's most wanted terrorists.
Taliban and al Qaeda leaders met near Pakistan's border with Afghanistan to confirm the new role for Adel, The Sun reported.
In response to the heightened threat on London, British Transport Police (BAT) are to be given the power to carry weapons on the capital's trains, stations and the underground for the first time.
Adel, whose name means Sword of Islam has been appointed as the caretaker leader of the terror group after bin Laden was killed in a US special operation at Abbottabad near the Pakistani capital Islamabad.
Transport secretary Philip Hammond will next week announce the plan, which is aimed at deterring the threat of another terrorist attack.
The BTP, which protects the rail, tube and urban metro system, has 2,900 officers and the proposals involve giving around 100 of them firearms training.
Security officials are particularly concerned about the possibility of an attack like that in November 2008 in Mumbai when gunmen attacked hotels and the city's main railway stations, killing nearly 200 people.
The news comes as the Manchester 'Easter shopping' bomb plot has been linked directly to Bin Laden for the first time.
Files seized by US special forces from the al Qaeda chief's Pakistani compound reveal that bin Laden himself masterminded the Manchester terrorist cell. The files have now been passed to MI5.
Twelve men - 11 Pakistanis and a Briton - were arrested over the alleged planned attack against Easter shoppers in April 2009. But authorities were eventually forced to set the alleged plotters free because of lack of evidence.
Last year, an attempt to report the group's alleged ringleader failed on human rights grounds because it was argued he would be tortured in his native Pakistan.
Documents found at the hide-out also suggested that al Qaeda planned to blow up oil tankers to spark an economic crisis in Western countries.