According to RAJA's latest figures covering Q2- interns of reach- (and courtesy of "Radio Today") the most listened-to Radio Stations serving London are as follows:-



BBC Radio 4 – 2.6m
BBC Radio 2 – 2.3m
Capital FM    – 2.2m
Magic 105.4 – 1.9m
BBC Radio 1 – 1.864m
Kiss             – 1.860m
Heart           – 1.837m
Classic FM    – 1.335m
BBC 5 live    – 1.306m
LBC             – 0.982m


Elsewhere:-
The same report also includes an interesting 'info graphic' detailing listening facts figures and methods.
It may be found here.

"The share of listening to DAB has increased by 1% to 24.1% of all listening.
26 million adults have access to a DAB receiver.

The role "Social Media" is playing is significant:-
38% of 15.24 year olds receive updates about their favourite Radio Station or presenter.
21% of adults receive updates about their favourite Radio Station or presenter.

Almost ten million people across the UK are listening to the Chris Evans Breakfast Show each week on BBC Radio 2.