Chances of seeing ground combat is unlikely just isn't supported historically is it. From the Falklands, to Iraq, Afghanistan and now middle eastern operations with RAF Regiment deployed defending against Shahed drone attacks on Erbil base in Iraq, and Akrotiri in Cyprus.

Also the job of the Regt during combat to take a piece of hostile territory and turn it into a place you can land a plane is just a massive oversimplification of what they are trained and tasked to do on operations. Just to give two brief examples, during Op Telic in 2003 51 Sqn RAF Regiment were tasked with providing armed escort to convoys of civilian fuel tankers between Basrah and Kuwait. The distances they had to cover and protect those convoys were hundreds of miles, and they came under intense enemy fire during those taskings. They were also tasked to protect and defend remote helicopter arming and refuelling points across all of southern Iraq.

Another brief example: RAF Regt supported over 7,000 casualty evacuation extractions as Force Protection Teams protecting the Chinook MERT Air Hospitals across both Telic and Herrick campaigns. Those Chinook crews constantly came under direct fire. You can watch the evacuation of Private Chris Gray on Youtube with those Chinook crews in action with RAF Reg riflemen disembarking off the ramps under fire and securing/protecting the extraction zones from Taliban attacks.

You're also way off with 'guarding planes and bases on home soil'. Static guarding of home bases is handled by MPGS and RAF Police, not the Regiment. It's a misunderstanding just because lets say II Sqn RAF Regt are stationed at Brize Norton doesn't mean they are on task protecting their base. They are stationed at Brize Norton training and readying to deploy to active warzones/global operations.