Video evidence of "Que signifie 1664?" is actually pretty hard to find - which just goes to show how much of an impact this campaign made.
So all credit to the great Matthew Harris, AKA Applemask, and Bob the Fish Productions for finding both adverts, in pretty decent quality, to feature in their "Hard Sell" series on Vimeo. (Skip to 27:07.)
This debate about whether banking groups like Lloyds or RBS should use just their own brand, rather than several, is obviously not TV related - but I'm going to add to it, while also mentioning another major ad campaign...
After Lloyds and the original TSB merged, of course, both banks were rebranded as Lloyds TSB. But just before the merger, Lloyds took over Cheltenham & Gloucester, and that brand remained on the high street until the creation of the current TSB in 2013. Lloyds had planned to close all the C&G branches a few years before - but before that, I assume that they too kept the brand out of loyalty and because C&G, as a former building society, offered something different.
Indeed, C&G's most famous ad campaign began shortly after the takeover - and was still going in 2003. While it probably didn't make *quite* the same impact that Howard did, it's nonetheless fondly remembered.