Theft is a big problem in the uk.
Tips
Keep it out of sight. In a garage or shed away from thieving eyes.
If it must be left out, you need a quality chain and lock. Not a cheapo Mickey Mouse one.
Never just put the chain through your wheel !
ALLWAYS chain the bike to something immovable, a street lamp, a heavy gate, metal fencing etc. if using metal fencing, chain through the thicker metal on the fence, or around the ground posts.
If the only fence available is poor, weave your chain through multiple poles.
Don't make it easy for the theif by securing to one skinny pole. Make it difficult to steal!
I've also seen people chain to low bollards, the theif simply lifts the chain over this, so try and think like a thief and do your best to put them off.
It is also better to chain through the rear wheel rather than the front one ( front wheels are easier to remove by thieves ) or better still, chain through your bikes frame
If these objects are not available and there are other bikes parked up, it's acceptable practise to park next to another motorcycle and link your security chain through their security chain.
It must be done in such a way that if the other rider returns, he can unlink from your chain.
It is not considered rude, cheeky, sassy to do this. Linking chains benefits both riders and offers greater security to both bikes.
One bike can be lifted into a nearby van by thieves. Two bikes joined together can not.
Watch out for people following you home. If you suspect being followed. Stop and allow them to pass, then take an obscure route home.
Bike alarm disc locks are a good cheap deterrent too. 120 decibels of screeching siren isn't nice. Remember to fit a telephone wire reminder between the lock and the throttle ! Riding off with a disc lock still in situ will see tears before bedtime !