Complex sentence: Many did, but a small number negotiated an exemption and remained Lib-Labs until 1918 causing ongoing disputes among members, but in 1918 the retirement of the remaining Lib-Labs and Labour's adoption of a programme championing nationalisation cemented the relationship.
Split into simpler sentences: Many did, but a small number negotiated an exemption and remained Lib-Labs until as late as 1918. This led to ongoing disputes among members, but the 1918 retirement of the remaining Lib-Labs and the adoption by Labour of a new programme championing nationalisation cemented the relationship.