Okay i have repeated the process.
The output of
apt-cache policy udev
looks like this:
udev:
Installed: 252.5-2~bpo11+1
Candidate: 252.5-2~bpo11+1
Version table:
*** 252.5-2~bpo11+1 100
100 Index of /debian bullseye-backports/main armhf Packages
100 /var/lib/dpkg/status
247.3-7+rpi1+deb11u2 500
500 Index of /raspbian bullseye/main armhf Packages
Unfortunately following command still fails