The monument honouring the 52 dead in the attack on London's transport system in 2005 cost nearly £1 million and has 52 stainless steel columns, 11.5ft tall.
It was unveiled in 2009 at a memorial attended by the Prince of Wales, the then Prime Minister Gordon Brown and other political leaders.
The columns are grouped together in four clusters, reflecting the separate locations of the bombings - Tavistock Square, Edgware Road, King's Cross and Aldgate.
More top news
The operation carried out by Westminster City Council led to the seizure of £8,000 worth of cigarettes.
Armed troops have been stationed around Parliament to free up armed police to patrol the streets in the wake of the Manchester bomb attack.
Chelsea had planned an open top bus tour to show off the Premier League trophy and hope to add the FA Cup in Saturday's final with Arsenal.