I’m tempted to advise you stick to CAVOK
Reality is there is no “safe” options in the UK due to these reasons …
Rapid weather changes at anytime of the year
Small country with significant terrain anomalies even in the so called flat bits
Complex airspace in the south limiting route options
Thus do what we all started with - pick your day carefully. If you must have a hard limit make it at least 2000 feet above terrain. Turn round and land if conditions worsen and thus build confidence slowly.
Which area are you based in?