You said the low beams sometimes work so it's not the bulbs...our Z-Cars are notorious for corroded electrical contacts...I suggest tracing EVERY connection from the fuses to the back of the headlights...wiggle 'em with the switch on and if the lights come on (or even flicker) you have found (at least one) poor connection
...it might be a good idea to pull every connection apart & clean the contacts too
...then apply dialectric grease & reassemble...I have an intermittant "high beams
out" and it is VERY frustrating...it is caused by the connection inside the steering column covers from the high-low switch to the headlight harness...someday I will have to replace it...hopefully your search will be a short one!!!

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