According to BEIS data, the total uptake of domestic heat pumps between April 2014 and December 2019 was 362. The uptake of the air source heat pumps was 298 and the uptake of ground source heat pumps was 64. Data can be accessed at https://www.gov.uk/government/statistics/rhi-monthly-deployment-data-december-2019-annual-edition
These statistics provide the number of heat pumps in receipt of the Government subsidy - Renewable Heat Incentive (RHI) programme. Whilst there may be some domestic heat pumps deployed without this incentive, it is expected that most would be in receipt of the RHI and therefore captured in this data.
In February I launched my Retrofit Accelerator - Homes which is supporting social landlords and boroughs in developing whole house retrofit approaches including upgrading building fabric and renewable energy technologies such as heat pumps.
Additionally, in 2018 my development policies in the London Plan resulted in 57 applications planning to install heat pumps. Cumulatively 235 have been proposed in applications since 2013.