With Mary Portas' recent review, the news that the high-street is obviously shrinking isn't 'news' any more. The British are the most enthusiastic online shoppers in the world, it's difficult to see a future for the high-street as a purely retail environment. Everything perishable is dealt with by the super-market. What's left - goods you have to touch: some clothing, but even ladies' clothes will struggle against the choice available online, A few artisan specialists such as Delicatessens and Butchers, and services. It's not about parking, it's about changing habits.
Get ready for high-streets containing even more by Accountants and Solicitors. Above all - leisure will dominate the future high-streets. Pubs, bars, restaurants, coffee-shops, bookies and casinos (have a look a this handy infographic - there will be a variety of provision for people wishing to gamble, especially in big destination towns like London) will replace shops as the dominant lessor of 'high-street' space. Towns will have to provide an appealing environment (and that, basically means no inner ring-road or 60's architecture) to attract visitors who're spending their time and money on themselves. For those towns lucky enough to retain a pretty mediaeval centre, and have sufficient property, there will be boutiques for tourists but they will be an anachronism.
Necessities will be sought from the super-market and online - the high-street of local shops is probably no-more.
"Save our shops". No more viable than save our coal-mine. The world, and technology has moved on.