Pheasant,
The terms strategic, operational and tactical get confusing very quickly when applied to 'actions' rather than 'levels of command'. Every action is 'tactical' when you boil it down to the kit and the operator; a SSBN manoeuvering into position and launching a salvo of Trident is undertaking a tactical action with distinctly strategic outcomes. Similarly, while the isolated act of flying a Typhoon out to intercept a Bear is tactical, the cumulative effect of many such acts over years is strategic (demonstrating that we remain prepared to meet potential incursions into our sovereign airspace). Nations that don't consistently show such resolve may find that they get overflown, and collected against, with impunity -a strategic failure to secure their own territory.
A Type 45 in the middle of the North Sea can do nothing to a Bear except broadcast radio warnings and/or shoot it down. Since aircraft have every right to fly in international airspace more than 12 miles offshore, those are empty threats unless open hostilities are already in progress. The Type 45 would have to let the Bear fly on by. Then, if the Bear did subsequently enter our territorial airspace, any missile fired by the Type 45 would be at long range and into congested airspace, with the Bear already having got into range to do whatever it was going to do. In contrast, a fighter can escort the Bear all the way into the territorial boundary, demonstrating the ability to engage with immediate effect, and able to observe visual cues of intent such as bomb bay door position. If you think shadowing foreign militaries near territorial boundaries is all about
PR, well, just look at what goes on daily in the East China Sea. It isn't.
Also, our handful of Type 45s are the air defence for the carrier group, and were not bought to defend our home territory - a job which can be done more sustainably from a fixed-base footing. Without the Type 45s, the carrier group would be reliant on its F-35s for air defence - the proverbial self-licking lollipop.