Sentence:  Both Thatcher's and Major's PPSs developed the role of trying to see that those members considered loyal to the leadership won the main positions on <WSD>backbench</WSD> party committees. 
Meaning of the word marked with <WSD> tags:  In a house of legislature following the model of the Westminster system (such as the UK House of Commons), any bench behind either of the front benches and occupied by rank-and-file members.