But they have an extremely strong law on their side: the
Proceeds of Crime Act 2002.
Part 5 allows them to use 'civil forfeiture' which means they can seize assets from people who aren't criminals using the civil courts and the civil burden of proof.
That means the police don't need to prove to the court that their target is a criminal 'beyond reasonable doubt', only that the funds were ill-gotten 'on the balance of probabilities' which is a far easier burden of proof to satisfy.
The police then apply for a CRO (Civil Recovery Oder) so the funds are repaid to the court & forwarded to the police, rather than repaid directly to the police. Which means if the target does not pay up they are in contempt of court - a criminal offence. At that point the courts can use criminal law to recover the CRO funds without the original offence needing to be a criminal one.
Even worse: if you're innocent and have a CRO served on you but win the case, it's almost impossible to recover your legal costs because the CRO was served through the civil courts rather then the criminal ones.