Marks & Spencer claim they introduced avocados to UK supermarkets, when they stocked them as 'avocado pears' in 1968. At the time, we Brits did not take to them.
People were confused by the name: when one customer complained after she’d stewed her avocado pear and served it with custard, M&S even started selling them with leaflets explaining they were intended to be a salad item.
Normal people shops, late '80s, early '90s mebbe? This potted history reckons 1968 for M&S (which is not a normal person shop when it comes to food):
A cultural history of the avocado