land drain, who maintains it

[nem39esis]

Bought a bellway home last year and have founf out that to the rear of my garden there is a land drain that drains my garden and my neighbours gardens. The gardens back onto a retaing wall around 2m high. The land drain is simply a perforated pipe with lots of gravel on top. So a chance the gravel could clog up and the garden not drain properly. My question is who maintains this as if it ever had problems, to replace it would be a huge undertaking. As i wasnt told about it either should i complain if it is my responsibility?