The investigation is lead by the Parliamentary Standards Commissioner. She recommends her findings to the committee, and they review the evidence and apply or over-rule her findings. So the committee are the appeals process, and the commissioner's findings and recommendations are always reviewed before being instigated.
The Parliamentary Commissioner for Standards is an independent officer of the House of Commons...
The Commissioner investigates allegations that MPs have breached the rules .....
The Commissioner also has oversight of investigations ... The Commissioner is the decision-maker for investigations ..., investigating allegations from the parliamentary community about harassment, bullying or sexual harassment by MPs.
The Commissioner keeps the Register of Members' Financial Interests.
The Commissioner ensures all investigations are independent, impartial, thorough and fair.
https://www.parliament.uk/mps-lords...sts/parliamentary-commissioner-for-standards/