London Government Act 1963

18 (1) If any person—

(a) knowingly erects or places any building, wall, bridge, fence, obstruction or encroachment in, on, over or under any sewer vested in the Greater London Council or in the council of an inner London borough ; or

(b) obstructs, fills in or diverts any sewer or drain vested in or under the control of, the Greater London Council or the council of an inner London borough,

without the previous consent in writing of the council in whom the sewer or drain is vested or by whom it is controlled, then, without prejudice to any other proceedings which may be taken against him, that council—

(i) may recover from him, as a debt due from him to the council, a penalty not exceeding twenty pounds, and a further penalty not exceeding five pounds for every day on which the contravention continues after notice thereof has been served on him by the council; and

(ii) may demolish and remove the building, wall, bridge, fence, obstruction or encroachment, and execute any works necessary for re-opening, restoring, repairing or reinstating the sewer or drain, as the case may be, and may recover from the offender the expenses incurred by the council in so doing.

(2) Nothing in this paragraph shall prevent or impede the maintenance, repair or renewal of any building or works under which a sewer or drain has been constructed, so however that the building or works shall not injure or obstruct the sewer or drain.