This was also posted on their FB page yesterday afternoon after some of the questioning by myself and others....
Tickets on the London PSO service beyond 28 March 2020 are expected to be on sale from the week commencing 6 January 2020.
Although you can currently only book travel on the service between Newquay and Heathrow until the end of March, the PSO service to London is contracted to operate 4 daily flights, 7 days per week until October 2022 and that commitment remains unchanged.
We are sorry for the inconvenience this delay to tickets being on sale is causing to passengers using the service but we are working with Flybe to optimise the route and ensure that Cornwall has the best available connectivity to London and beyond.