The Highways Agency is to review drainage systems used on the M25 London orbital motorway after chronic flooding closed part of the UK's busiest road for seven hours on Monday. A spokeswoman said: 'We will be looking at the whole drainage system, and will consider whether any additional work needs to be done'. Water flooded to a depth of over 1m on the anti-clockwise carriageway between junctions 9 and 10 before spilling over on to the clockwise carriageway. Leaves, windborne debris and soil clogged the drains after rain fell on embankments already saturated by heavy rainfall over the weekend. Fire crews and contractors pumped water to clear the carriageway, which was re-opened at 2pm on Monday. The closure caused traffic chaos from 7am. The spokeswoman added: 'The drainage system was flooded at full capacity, and was not designed for falls of this nature.'