Garden flooding - 4 properties

Two surface water sewers from our garden connect to the M27 drainage network at Junction 10. One is heavily silted. The other has collapsed, almost certainly due to root damage from a huge willow just beyond our rear fence on the slip road embankment. The result is severe garden flooding across 4 properties whenever there is prolonged rainfall. This problem has existed for over two years, but responsibility only recently assumed by National Highways. The silted sewer needs to be cleared and the collapsed sewer repaired.