Cannot access some websites after latest Monterey upgrade

Updated MacBook Pro to MacOS 12.4, Safari 15.5 yesterday.

Now unable to access some websites on Safari. Everything OK on Chrome on same machine and on old iMac (MacOS 10.15.7, Safari 15.5), and iPhone on IOS 15.5. Identical problem however on iPad running iPadOS 15.5.

Two sites I cannot access properly are www.ramblers.org.uk - it loads nothing.  I can load www.bridgebase.com but cannot access anything from that page including the login. I used these sites daily until last week with Safari on MacBook Pro. These are the only two problematic sites I have seen so far but I have not been onto all the sites I use.