The report stated that shorter scheme membership could explain part of the gap.
Pension outcomes for disabled and non-disabled members were broadly similar, with disabled members accruing 0.4% more.
Generation Z had the lowest participation rate, with 74% of Generation Z men taking part in the scheme.
Charlotte O’Leary, chief executive of Investors for Purpose, said: “Westminster City Council and the City of Westminster Pension Fund deserve real credit for commissioning and enabling this research.
“The gender pension gap in our Westminster case study being substantially below the wider LGPS level is encouraging, and it demonstrates what is possible when employers and schemes commit to understanding the real-world issues that their members face.
“This research also shows why pension savings gap research and analysis beyond pure reporting is needed.”
O’Leary added: “When taken together and looking at the interaction between and across gender, ethnicity, disability and generation, the picture becomes more complex and more nuanced reflecting a need to understand root causes and systemic impacts before setting policy.
“I believe, for example, that an LGPS-wide ethnicity benchmark would be transformative based on the research.
“It would give every scheme and employer the ability to understand their own position, identify where action is needed and track progress over time.”
She said: “We are often told that we don’t have the data, but Westminster’s leadership in this has proven that the data can be gathered, analysed and acted on.
“Investors for Purpose is committed to understanding inequality as a systemic risk and opportunity that can be addressed, and we want to continue our work with leaders in this space to support in developing systems that provide the best outcomes for all people and our planet.”
Clair Alcock, SAB secretary, said: “I am proud that the LGPS is the first public service pension scheme to have made gender pension gap reporting business as usual.
“What this groundbreaking research shows is that, if we are serious about understanding inequality in pension outcomes, gender alone is not enough.
“By examining ethnicity, disability and age alongside gender, the report begins to build the evidence base needed to drive meaningful change.”
Alcock added: “I would encourage Ministers to build on this progress by extending pension gap reporting to other protected characteristics and across all public service pension schemes.”
Gerald Almeroth, executive director, finance and resources at Westminster City Council, said: “As a Scheme Employer within the City of Westminster Pension Fund, Westminster City Council was proud to support this work by providing employer data and insight.
“The findings will help strengthen our understanding of where pension gaps exist, what drives them and how employers, funds and other stakeholders can work together to improve engagement, inform policy development and ensure more people can fully benefit from the valuable retirement security offered by the LGPS.”
Greer Flanagan, partner at Hymans Robertson, said: “We’re very proud to have contributed to this report which takes the important next step in highlighting diversity pension gaps by considering ethnicity, disability and gender gaps.
“The report helps us to better understand the barriers that make it harder for some people to build long-term financial security and identify ways to address them.
“By bringing these challenges into sharper focus, more informed action can be taken across the LGPS and beyond.”