In 1971, Tilley was elected to Wandsworth Council, where he became council leader. He was selected as Labour candidate to fight Kensington in the February 1974 and October 1974 elections, with improving results but no success. The party chose him to defend at a by-election its long-standing high majority in Lambeth Central in 1978, which he won. The election was triggered by a caused by the death of Labour MP Marcus Lipton. In Parliament, he served on Labour's opposition front bench, resigning in 1982 in opposition to the Party leadership's stand on the Falklands War. As MP for the Brixton area, he worked with Lord Scarman after the 1981 Brixton Riots for a better understanding of local social problems. He proposed a bill to amend the Sexual Offences (Amendment) Act 1976 to make rape in marriage illegal in 1983.