The police these days are very risk conscious.
The fact that they have got a 'phone call from you before you go out won't necessarily stop them sending out firearms officers, dogs, helicopters, a troop of morris dancers and a tea lady when someone calls in and says there's a mad man on the loose shooting up the countryside, probably part of a terrorist cell practicing. They might call you to try verify whether it's you or not, but most people will have the phone on silent or be in some leafy valley or fell with no signal. The caller to the police will no doubt have exaggerated the situation to justify himself and the police are left with a decision. Do nothing and face the consequences if something is wrong or send out the circus to make sure their backs are covered.
So don't think the magic 'phone call is a cure-all. There are times when it might be advisable to tell the police. There are times when it's a waste of time. That decision should be down to the individual. I expect most police forces don't realise how many calls they'd get if everyone did it or it was made compulsory. Imagine the deluge of calls during the pheasant season every weekend, the keeper doing his rounds daily, rough shooters, stalkers, vermin controllers, people zeroing their rifles, wildfowlers and those just taking a clay trap into a field.