Consultancy Turley's report, Making sense of mixed-use town centres, also warns that the government's proposed changes to permitted development (PD) rights and high street use classes risk a "haphazard" approach to town centre development.
The study reviews the challenges facing high streets and the likely impact of proposed policy changes.
It examined the potential of re-purposing the 8 million square metres of vacant commercial floorspace that it claims currently exists in town centres across the UK into a range of different uses.
"We estimate that if one third of vacant floorspace in town centres was re-used for residential purposes, at least 45,000 new homes could be created. This is very much a minimum capacity working on the assumption that new residential developments do not exceed the height of existing buildings."
The indicative capacity figure "could be increased, or easily doubled, if on average one or two additional storeys were added to the space recorded as vacant," it adds.
Some 15 per cent of vacant floorspace could be used for A1 retail, while the same proportion could be used for leisure-based uses and again for employment, according to the study.
The report warned against discounting retail when planning for town centres and said rumours of the "death of the high street" have been exaggerated.
While the average annual percentage of retail sales taking place online has risen dramatically, from 3.4 per cent to 18 per cent between 2008 and 2018, the report found that in-store sales in 2017 were still four times higher than online spending.
Elswhere, the report says the government's proposed revisions to planning rules on use class changes in town centres, which apply to England only, "could help to encourage a reinvention and reverse the fortunes of ailing high streets".
However, the firm also claimed it "risks a haphazard approach to mixed-use town centres arising, where design quality and liveability suffer".
In particular, "many challenges could arise" if policies such as broader PD rights and the merging of use classes are applied to all town centres, regardless of whether they are currently performing well, the report said.
In response to the proposals, Turley called for councils to put in place "common sense checks" and local frameworks to make sure changes to town centres are "comprehensive and not piecemeal".
Last month, leading sector bodies responding to a consultation on the proposed changes to high street planning policies warned of a range of potential unintended consequences - without making life easier for developers.
Critics have also raised concerns that a new use class merging shops, financial services and restaurants could mean councils losing control over town centre development.
In July last year, the government announced a High Streets Task Force to advise on how to ensure the future vitality of town centres.