The successful Sinn Fein candidates in Fermanagh & Tyrone South and Ulster Mid had both been imprisoned for their part in a raid on Omagh, and were therefore ineligible for election to the House of Commons. In Ulster Mid a new writ was issued for a by election that was held on 11 August 1955.

Following the by election, Mitchell was again disqualified on petition to the Northern Ireland High Court due to his imprisonment and on 7 October 1955 Beattie was declared elected in his place, although he didn't take his seat. On further petition to a House of Commons Select Committee, it was ruled on 7 February 1956 that Beattie was disqualifed for holding "offices of profit under the Crown" (membership of national insurance and national assistance tribunals), and a second writ was issued for a by election on 8 May 1956.