Lots of options.
I have a degree in criminology, was a police officer including a Detective for a decade, spent another 5yrs in an unrelated type of criminal prosecutorial and investigative role and ended up here (deliberately not saying where).
I work with people in the same role with no degree, others in their first job out of university, ex-military, ex-police or prison officers.... Huge variation in experience, age and paper qualifications. We work on increasing the intelligence, interpreting it, analysing it, identifying what is missing from the picture, applying for RIPA relating to phones and CCTV, applying for authorities to carry out surveillance, organising banking or other financial enquiries and directing the teams who do that. All sorts of other stuff.
I would say we carry out swathes of pure criminal investigation in the same way as a police officer, as we hand over full packs including statements, evidence etc which just require someone with a warrant to carry out arrests and searches.
Have a look at the Civil Service Jobs website for the keyword "intelligence" and see what you see. Lots of CS agencies have intelligence departments, although not all of it is criminal intelligence. Several colleagues started as a Collator then Analyst then Lead Analyst then departmental heads etc. NCA, MHRA, HMPPS, Forestry England....
There's also police intelligence work, but they don't pay as well!
I'd love to work in the Cabinet Office JIO, but it would require me to work in Central London every day and it doesn't pay enough for me to afford to live up there. I currently am able to do a huge amount of work remotely.