A summary of the 2019 costs to watch F1 in the UK can be found
here.
In short, every method requires a TV Licence at a cost of £154.50, which was the case when F1 was broadcast as FTA.
On top of this, the cheapest way to watch every F1 race in the UK was a further £76.93 for the season if using a mobile device, £179.80 on a TV, or £404 if you don't have an internet connection.