The Guards are real soldiers. Not sure why they need extra troops to guard Buckingham.
To be fair, the Guards are inside the gates/fences.
The regular police had to arrest a knife-carrying thug about 200 yds away this morning. Sounds as if he was just a garden-variety cretin whose ignorance of the news and in general landed him in far more trouble than it would have done last week.
I think they don’t want the “changing of the guard” crowds around Buckingham Palace right now.
So, they replaced them with camouflage suited troops to do the same job.
And besides, it makes it look like they’re actually doing something substantial and important. (which they are not)