It’s been asked many times but in short no.
there was a limited potential call up when officers were VRT (mainly centred on specific roles & trades) but in short we would all be stood down under current regulations,
However in the event of a military attack on the uk from a hostile state I suspect with staffing requirements as there are, there may be some quick legislation kicking in.
The emergency powers act is quite powerful if ever invoked.
Closest we got to a national emergency was Covid & then resulted in a stop everything so they didn’t have to concentrate on cadets mindset.
Whilst it is scary I wouldn’t worry too much & would try to avoid getting caught up in the hubris