The twentieth century constituency was created in 1918 and remained virtually unchanged until its abolition in 1983. The territory included in the new seat was similar to that previously constituting the Wisbech constituency (the Northern division of Cambridgeshire). That constituency was dominated by the Fens, a district of Liberal inclined smallholders. The towns in the Wisbech division, predominantly Conservative Wisbech and the more Liberal inclined March, tended to be outvoted by the rural areas.
The small city of Ely had formerly been part of the Newmarket constituency (the east division of Cambridgeshire). Pelling suggests Ely was Conservative "because of the cathedral and its fairly substantial middle-class population".
In 1918, the former Liberal MP for Wisbech, Colin Coote, was returned unopposed as a Coalition Liberal. In 1922 Coote contested the seat again, this time as a National Liberal candidate. A Labour candidate appeared for the first time. The anti-Conservative vote was badly split (National Liberal 27.7% and Labour 21.4%), so the Conservative soldier Lieutenant Colonel Norman Coates was easily elected. Coates retired and did not seek re-election in 1923.
In 1923, the reunited Liberal Party nominated a member of the family of one of their richest members. Henry Mond was the son of the industrialist Alfred Mond (later the 1st Lord Melchett). He was able to squeeze the Labour vote down to 12.4%, which was sufficient for a narrow Liberal victory as part of the party's best election result after the First World War.
In the 1924 general election, both the Conservative and Labour candidates increased their vote. Mond was defeated. The new MP was the Conservative, Sir Hugh Lucas-Tooth, Bt. Lucas-Tooth had a long political career, not leaving the House of Commons until 1970, but he only retained this seat for one Parliament until his defeat in 1929.
The Monds had joined the Conservative Party in 1926 after a disagreement with Lloyd George's land policy. However another rich Liberal stood in this constituency in 1929, the flamboyant James de Rothschild. He retained the seat for three Parliaments, serving from 1929 to 1945. In the 1945 general election de Rothschild came third, the first time this had happened to any Liberal candidate in the constituency.
It must have appeared that the days when the Isle seat was a Conservative/Liberal marginal had ended in 1945. The new Conservative MP, Harry Legge-Bourke, had a majority of 6.1% over Labour, with the Liberal almost 10% further behind. He retained the seat until his death in 1973, with Labour in second place. The Liberal Party did not contest general elections in 1951, 1955, 1959, 1964 and 1970. The Liberal vote in 1966 was only 11.4%.
Clement Freud gained the seat for the Liberals from the Conservatives in a 1973 by-election during the height of the 1970s Liberal revival. He retained the seat until it was abolished in 1983 and won the successor seat of North East Cambridgeshire that year, but was defeated in 1987.
The constituency was renamed in 1983, with most of the territory incorporated into the constituency of North East Cambridgeshire.
In 1965, the Isle of Ely county was merged into the new administrative county of Cambridgeshire and Isle of Ely and in the next redistribution of parliamentary seats, which took effect for the February 1974 general election, the constituency was defined as comprising:
The only change was the loss of the small rural district of Thorney, which had been included in the new administrative county of Huntingdon and Peterborough and was now transferred to the borough constituency of Peterborough.
Meanwhile, as a result of the Local Government Act 1972, the two counties of Cambridgeshire and Isle of Ely, and Huntingdon and Peterborough were merged to form the non-metropolitan county of Cambridgeshire, with effect from 1 April 1974. However, the next redistribution did not come into effect until the 1983 general election, when the constituency was largely replaced by North East Cambridgeshire. The city of Ely was included in the new constituency of South East Cambridgeshire, and the villages of Thorney and Eye were returned from Peterborough.
