The Home Office collects information from police forces on the number of police recorded offences that have an online element. The online flag became mandatory from April 2015 therefore data prior to this are not available.
Information on the number of child sexual offences flagged as having an online element are published as experimental statistics in the ONS ‘Crime in England and Wales’ quarterly bulletins. The ‘child sexual offences’ category includes sexual grooming. Information on sexual grooming is not separately published.
These data can be found in table E12 of the experimental tables on the ONS website: https://www.ons.gov.uk/peoplepopulationandcommunity/crimeandjustice/datasets/crimeinenglandandwalesexperimentaltables.
The Home Office does not hold information on the number of online child grooming offences which have led to prosecutions. The Ministry of Justice are responsible for prosecutions data.