A lot of things killed the high st. Rates were probably the biggest initial slapdown. Most shops in my high st went because the rates got ridiculously high, and unsustainable, even for the bigger shops. Supermarkets took advantage of this to an extent and gave high st shops another kick. This started in the 70's and picked up speed as time went on. Bookies, pubs, carry outs, and charity shops are pretty much all we have in our town of over 20k.
As my dad said a few years b4 he died, the councils got greedy and kicked themselves into touch. I might add the small shops didnt help themselves as they didnt want big competition coming in, stating it would take all their trade, which was rubbish. bringing in some big name shops would have increased trade for all. Think there is only one original shop left now(a butchers)