Speeding is also a criminal offence...
Just think for a moment why murderers are incarcerated over other matters that are criminal offences. It's not difficult to understand.
Speeding is not a serious criminal offence. The maximum penalty for speeding is a £2,500 fine.
Meanwhile, tax evasion carries a maximum sentence of 10 years in prison.
One criminal offence carries a custodial penalty, the other does not. Do you understand the difference?