Having read the briefing paper 07212
https://researchbriefings.files.parliament.uk/documents/CBP-7212/CBP-7212.pdf

I draw your attention to the section highlighted in red. The legislation contained no mention of a threshold. As the referendum was "advisory" there was no necessity, it was to be treated as indicative.
Had it been as you suggest the newspapers would have been on the case like rats up a drainpipe.

The Bill does not propose a threshold for the referendum. The only referendums held in the UK where a threshold has operated were the polls in Scotland and Wales in 1978 on the question of devolution.65
Discussion of the need for some form of threshold usually arises in the context of ensuring the legitimacy and acceptance of the outcome of a referendum. Certain states require constitutional change to be validated by a special majority in a referendum. This incorporates the idea that major constitutional change is something more important than the result of ordinary elections, and therefore should be the outcome of something more than a simple plurality of the votes. The UK does not have a comprehensive written constitution and so any requirement for a threshold has to be included in the individual referendum legislation. Standard Note 2809 Thresholds in Referendums gives further details and provides comparative examples of the use of thresholds.