YABVU
If you really wanted to improve safety, you'd ensure that everyone could access free cycle training, and make it compulsary for all car drivers to do a cyclist awareness course (which included the experience of riding a bike on-road) in order to hold a driving licence.
<nb: all-abilities cycling exists! there are plenty of ways this training could be delivered for those who cannot ride a bike themselves for whatever reason>
You'd also ensure that there was a network of properly designed, joined-up infrastructure for cyclists that could be safely used by anyone from ages 8-80 <the knowledge and expertise needed to do this exists - look at the Netherlands or even London for examples of good-quality, well-planned cycle routes - but the political will is lacking in most parts of the UK - building them costs much less than other kinds of roads, motorways etc>
It would also be helpful to change the law around liability so motorists who injured vulnerable road users faced stricter penalties here (as happens in other countries).
Yes, there is a lot of publicity whenever a cyclist's actions lead to the death of a pedestrian - as PPs have said, this only happens about once a year - and the cyclists responsible have done time in jail. However there are far too many deaths caused by the drivers of larger vehicles (usually 400-500 per year) when the driver doesn't even permanently lose their driving licence, never mind go to prison.
As most other people have said, vehicle tax is based on emissions, so cyclists wouldn't actually pay anything. The costs of admministering such a scheme make it prohibitive. Same as licensing the people who ride bikes. Every single study done by the Dept of Transport and others has suggested it's a bad idea, which is why, despite the occasional mindless witterings of Tory party politicians and other arrogant characters, it's not going to happen.